Frankincense essential oil and cancer:
Why EOs and chemotherapy don’t always mix

My friend just started taking chemo for colon liver cancer and she was taking therapeutic Sacra Frankincense from Young Living before she started. I read somewhere that you should not take the essential oil with 5FU if you are taking it for skin cancer because it will drive it in the skin deeper and make the chemo 10 times greater. That sounded good to me, but for some reason they say not to use Frankincense with 5FU. Since she has colon liver cancer, and not skin cancer, should she just rub it on her feet and side, stop taking it, or take it internal, or not at all. I am not sure how to direct her at this time, but she has heard so much good about the Sacra Frankincense killing the cancer cells. Any help or suggestions would be welcomed and appreciated. Also, have you heard anything about stopping essential oils when you are on chemo. Someone also said, stop 2 days before your treatment and then start back 9 days later. My friend takes chemo for three days in a row using a pump and then 14 days later she starts again, so it gives her no time to use her oils.

My thanks,
Patti F.

Hi Patti,

Many essential oils have protective & antioxidant effects on our cells, and there is a reasonable chance that they will do the same for cancer cells – protect them from the chemotherapy – which of course would not be a good thing. This opinion is shared by many. It probably sounds odd – you’re thinking that frankincense oil should kill cancer cells and not protect them – but the only evidence for killing cancer cells (apart from one skin cancer report) comes from a few lab tests when high concentrations were used.

Moderate amounts of EO will not kill cancer cells, but could protect them. And taking large amounts of essential oil could very well interfere with the chemotherapy itself, by increasing or decreasing the concentration of drug-metabolizing enzymes in the liver. By causing a chemo drug to be metabolized more quickly, you reduce the duration of its effect. On the other hand if you inhibit its metabolism you reduce the efficacy of the drug. Neither of these is desirable, and chemo drugs are very carefully dosed for each patient.

For all these reasons, I suggest avoiding essential oils for one week before until one month after chemotherapy. After that time, frankincense oil may help with recovery of white blood cells, as also spearmint, dill and other essential oils.

Incidentally, almost all of the research on frankincense and cancer is on the extract, which contains boswellic acid, and not the essential oil, which does not. Frankincense extracts contain around 50% boswellic acid, which is a widely-studied antitumoral agent. However, getting such remedies to the target site in sufficient concentration to be effective is a challenge.


Thank you so much for the info and for taking the time to help in this matter. I will let her know to immediately stop the Frankincense until she is finished with the chemo.

Lavender mascara?

Adding lavender oil to your mascara has become a thing, on the basis that it will make your eyelashes longer and thicker, and also that it will deter eyelash mites. About half of us have tiny eyelash mites, but they don’t affect at least 95% of those who have them. They do not make your eyelashes thinner or shorter, though an infestation can make eyelashes fall out. Some argue that eyelash mites perform a useful function, by eating dead cells and debris. If the mites do indeed proliferate, the condition is known as demodicosis. This can happen in people with a severely deficient immune system, and there are significant associations between demodicosis and certain inflammatory skin conditions, especially some types of rosacea.

Demodicosis is treatable with tea tree products (ointment, shampoo, washes), in fact this is one of the most effective treatments known. For daily use, there is a product based on terpinen-4-ol, the major constituent of tea tree oil. This used to be only available to dermatologists. By all means use this or tea tree products for daily hygiene, but unless you have demodicosis, trying to totally eliminate eyelash mites that you can’t see may be pointless.

Woman applying mascara on eyelashesAs for lavender mascara, there’s no evidence that lavender oil has any effect on eyelash mites, eyelash length, or eyelash thickness. Adding lavender oil to your mascara is not necessarily dangerous, but it could be if it’s not evenly distributed. How do you mix the lavender oil in the mascara? The packaging and consistency of the product make even distribution of an essential oil challenging. And why are you doing it? Even if you add tea tree oil instead of lavender to your mascara, it’s not likely to have much effect on eyelash mites (which you might not have anyway). Maybe it will keep them off your lashes, but it won’t get to them where they spend most of their time – inside your hair follicles. So my advice is, don’t mess with your mascara, but maybe look out for tea tree face washes.

A word of warning – do not apply undiluted tea tree oil, or any other essential oil, to your eyes – very bad things can happen! (In one of the above links you will see “apply a couple of drops of tea tree oil to the lashes”. Don’t!)

Bergamot Oil – Toxic To Children?

I was recently contacted by an essential oil business (Plant Therapy) which had several customers ask about the safety of bergamot oil, as they had heard it could be lethal and cause convulsions in children. The sources of this warning appear to be and, as both websites have profiles on bergamot oil that include this:

“Do not use bergamot oil in children. There have been serious side effects, including convulsion and death, in children who have taken large amounts of bergamot oil.” These are no doubt widely-read websites. The WebMD information is quoted by Wikipedia. Both websites give the following source for all their information:

This copyrighted material is provided by Natural Medicines Comprehensive Database ConsumerVersion. Information from this source is evidence-based and objective, and without commercial influence. For professional medical information on natural medicines, see Natural Medicines Comprehensive Database Professional Version. © Therapeutic Research Faculty 2009.

Citrus bergamia

Citrus bergamia

The Therapeutic Research Faculty (TRF) is based in Stockton, California and sets a high standard for its own ethics.

After subscribing to the Natural Medicines Comprehensive Database ConsumerVersion (NMCDCV), I found the following: “Bergamot oil is POSSIBLY UNSAFE in children when taken by mouth in large amounts. There have been serious side effects, including convulsion and death, in children who have taken large amounts of bergamot oil.” However, still no information source is given. This is frustrating, especially for a website that claims it is wholly evidence-based. The TRF website has this: “All data and recommendations by the Center and any of its publications are based on scientific data. Therapeutic Research Center supports the key elements of evidence-based medicine.” An outline of evidence-based medicine can be found here. If the NMCDCV or the TRF have any evidence for their assertions, they are certainly keeping it well hidden.

No cases of child poisoning from bergamot oil are evident on any publicly accessible database. All the available information indicates that bergamot oil is non-toxic, and to the best of my knowledge, there are no reports of poisoning, or convulsions, or death, in either children or adults. Bergamot oil has GRAS (generally recognized as safe) status. There are no safety cautions for either children or systemic toxicity in either the Merck Index, or in Martindale, The Extra Pharmacopoeia, and these are standard reference works for such reports.

The acute toxicity of bergamot oil in rats was found to be over 10 g/kg (Opdyke 1973). This means that at 10 g/kg there were no rat deaths, so the lethal dose was something greater than this, and 10 g/kg is equivalent to 700 g (24.7 oz) in a 70 kg (154 lb) human. This is an extremely non-toxic substance! I am not aware of any evidence that bergamot oil is convulsant, either in lab animals or humans. In fact its main constituent, limonene, is anticonvulsant (Carvalho-Freitas & Costa 2002, Sayyah et al 2004).

The caution in the NMCDCV is not backed up by any scientific evidence, and makes no sense in light of everything that is known about bergamot oil. The website does invite “comments or suggestions on something that should be reviewed or included” but clicking here brings up a box that says: “Use this form to e-mail technical questions to the web site designers. For medical questions or any other questions about the use of any of the products listed on this web site, please contact your health care provider. (Bold type not mine).

sloppy science

So is bergamot oil safe to use on children? We know that the oil is not acutely toxic, and all of the major constituents (limonene, linalyl acetate, linalool) and most of the minor constituents of the oil are known to be safe in terms of systemic toxicity (Tisserand & Young 2013). So a truly massive amount would have to be used in order to produce serious toxicity. A 3 year-old child weighing 14 kg (31 lb) would have to drink 140 g (4.9 oz) to attain the 10 g/kg level that was not quite lethal in rats.

No cases of bergamot oil poisoning have been reported, perhaps because few consumers possess large enough bottles of bergamot oil, and even if they did, that’s a lot of essential oil to drink! Bergamot oil is photosensitizing (see Safety note below), and this is a very important issue in terms of skin safety, but otherwise there is no particular reason for caution in children. There are a few moderately toxic essential oils, but bergamot oil is not one of them, in fact it is one of the least toxic of all essential oils. In my opinion, the claim that bergamot oil can cause convulsions and death in children is baseless and irresponsible.

Safety note
Bergamot oil is photosensitizing, meaning that if applied to the skin at certain concentrations, burning can occur if the skin is also exposed to ultraviolet light. To avoid this, bergamot should not be used at more that 0.4% dilution on the skin, or if it is, the person should not go outside during daylight for 12-18 hours (Tisserand & Young 2013). Alternatively, bergapten-free bergamot oil can be used, as this is not phototoxic. This warning applies to “leave-on” preparations such as oils, lotions and balms. There is no risk from “wash-off” products, such as soaps, shampoos and bubble baths.

Carvalho-Freitas, M.I., Costa, M., 2002. Anxiolytic and sedative effects of
extracts and essential oil from Citrus aurantium. Biological &
Pharmacological Bulletin 25, 1629–1633

Opdyke, D.L.J., 1973. Monographs on fragrance raw materials. Food &
Cosmetics Toxicology 11 (Suppl), p. 1035

Sayyah, M., Nadjafnia, L., Kamalinejad, M., 2004. Anticonvulsant activity
and chemical composition of Artemisia dracunculus L. essential oil. Journal of
Ethnopharmacology. 94, 283–287

Tisserand, R., Young, R., 2013. Essential Oil Safety, Churchill Livingstone, Edinburgh, p. 211

China Report 2014

On Thursday July 24th, I left home for my second visit to the People’s Republic of China! (see report and video of my first visit here, and pics here) This time I was invited by a Beijing-based aromatherapy school, Floralwish. The most obvious difference from my 2011 trip was the weather – instead of November’s freeze, I encountered a very warm and humid August, with average temps of around 90F. And this time, after my weekend seminar in Beijing, I was going to repeat it a week later in Shanghai, providing time for some sightseeing in between.

After my 13 hour Air China flight I arrived in Beijing at 5.40 am. Ellen, the Floralwish owner, and Orange and Joanna, my guides for most of my stay, took great care of me, and welcomed me with an immaculate placard! After a 90-minute drive across the city we arrived at the Lakeview Hotel, which would be my home for the next few days as well as the venue for the first seminar. The hotel is a part of Beijing University Campus and is busy with guests and conferences. It has an amazing courtyard garden with waterfalls, duck ponds, lotuses in flower, and tress that included apricot, weeping willow and gingko biloba.

Lakeview hotel gardens

In the afternoon I met with Liza, who would be my translator for both the events. (People in China often try to make it easier for us to remember their names by choosing a westernized one.) Liza has a degree in TCM and specializes in cancer treatment. When we met she had already taken extensive notes, especially for the names of constituents. We were able to run through the presentation quite quickly to make sure everything was clear.

RT in ChinaFriday was a day of rest and final preparation for the event, and on Saturday morning I made my way to the seminar room. The 65 attendees arrived at 10.00 am, keen to acquire new information about how to use essential oils with minimal risk. On the first day I covered general topics such as the difference between hazard and risk. I used an analogy about crossing streets in Beijing – there is hazard, but various factors increase or decrease actual risk (such as speed of traffic, amount of traffic, and how good your vision is).

I also talked about different types of evidence (in vitro, in vivo, clinical etc), and the different methods of administration and their specific constraints. There was a lively discussion about long-term inhalation. I recommend that a 30-60 minute period of inhalation should be followed by inhalation of “clean air” for the same amount of time to avoid adverse effects. I call this intermittent inhalation, or diffusion. For very low levels of fragrance, barely perceptible, it’s not important.

We also discussed the pros and cons of patch testing in some detail. In general, I don’t feel it is necessary unless there is a known problem. At the end of the day there was a group discussion and revision of all that had been covered.

On Saturday night there was a special gastronomical treat. The organization team and translator, four amazing women, took me to a popular “hot pot” restaurant. Set into the middle of the table were two rectangular containers filled with seasoned water, one spicy and one not, placed over gas burners. As the evening progressed, various foods were dropped into the boiling water – from chicken, lamb and beef, through tofu of all kinds and forms to duck tongue and a cuttlefish meatball, which was quite delicious. We were also treated to what might be described as a “noodle dance”, similar to the tossing of pizza dough. One of the staff appeared by our table and proceeded to stretch out flat noodles made of tofu till they were perhaps 6 feet long, at the same time dancing them through the air in fast-moving ribbons. He then deftly shortened them with his (gloved) fingers, and tossed into the boiling pot. I was impressed, and the noodles were very tasty.

Dinner in China

Back at the seminar on Sunday, we successfully negotiated the safety aspects of some weight subjects including cancer, pregnancy, drug interactions and phototoxicity. We paused occasionally to make sure that plant names were being correctly translated (botanical names are not much used in China), and there were questions about the use of wintergreen oil together with blood-thinning drugs. The issue of whether and which essential oils can be used to help treat cancer was raised. In response to this I talked about research on perillyl alcohol (mainly for brain cancer) and Zedoary (Curcuma zedoaria) essential oil (liver cancer). Perillyl alcohol is a constituent of Perilla frutescens oil, which is produced in both China and Japan, but is not well known outside Asia. See more on this emerging research. As always in Asia, there was an extensive photo session after the event.

There was a pre-arranged magazine interview on Monday afternoon with Modern Brides. The editor wanted to know the various ways that essential oils could be used to help married couples. She asked many questions in the area of relaxation, mood changers, aphrodisiacs, and which oils would revive a “tired” relationship. At one point I talked about creating an “anchoring” blend by using it during a vacation to build an association with feeling good, and then afterwards bringing out the blend only when really needed. I also suggested that a blend of bergamot, sandalwood, frankincense and jasmine would be useful for “feelgood” and sensuality. After the interview we drove into the center of Beijing for lunch, and to visit the Floralwish premises, which are located in a Hutong area.

On Tuesday, Orange and Joanna took me to the Great Wall, specifically to a part called Badaling. As we approached the area, hills seemed to suddenly spring up, and then we could see the wall hugging both peaks and valleys. It is of course a stunning feat of engineering, with millions of heavy stones perfectly laid across hilly terrain. This section was built in 1504, and is maybe a mile in length. Very few sections are flat, and some are very steep, and stepped. After a couple of hours of wall-walking (to the end of this part and back again) we had a much-needed lunch, and then drove back into Beijing.

On Wednesday I visited Darren Moore and his family. Darren had been my host in 2011 and it was great to see him again. He is Canadian, and settled in Beijing when he fell in love with a local girl. As well as making natural soaps and cosmetics (he does not even like to use emulsifiying agents for lotions) his mission is to inspire others to return to a more local, organic and small-scale style of living. New to me was a walled vegetable garden, where he has green beans, fruit trees and a lot of sweet corn. We visited a local park where we saw hundreds of coi carp in a pond being fed. For dinner we drove to an artists district where we ate lamb skewers and some delicious thin, black noodles made from fern. Thursday was another rest day, and Friday was a travel day.

Due to some political issues, many domestic flights in China were delayed or cancelled so it was decided that we would take the train to Shanghai instead of flying, as had been planned. At Beijing train station I said goodbye to Ellen, who would not be coming to Shanghai. The journey was fast and smooth: traveling at 200 mph, it took only 5 hours to travel almost 1,000 miles and we crossed the two longest bridges in the world, the Danyan-Kushan Grand Bridge and the Tianjin Grand Bridge. As we traveled through the city of Nanjing I discovered that the name means “capital of the south”, while Beijing means “capital of the north”. After a long drive from the train station we arrived at the hotel, which again was also the venue for the seminar. My room at the Wyndham Bund East Shanghai hotel had stunning views of the Huangpu river and the Yangpu bridge that crosses it.

Shanghai is different to Beijing in many respects. The architecture is more European, the air is less polluted, and the food is sweeter and less spicy than in Beijing. Unfortunately, I found the espresso coffee in the hotel undrinkable, but the choice of rice, tofu, veggies etc at breakfast was very welcome, as it had been in Beijing.

There were 30 attendees at the Shanghai seminar, including, unusually, 5 guys. A few participants spoke excellent English and one lady had travelled from the Philippines for the event. Liza was already familiar with my material of course. Among the questions asked was the issue of fennel oil and its probable estrogenic action. We know that fennel tea, apart from relieving colic, promotes production of breast milk, and I have recommended that the oil should not be used in either pregnancy or breastfeeding. I am now wondering if I should reconsider my breastfeeding ban for fennel oil.

Shanghai group photo

Sunday was my last evening in China and I was given a spectacular send-off. Dinner was in a Thai restaurant in the exciting Bund area of Shanghai, which at night is spectacularly lit. The restaurant was on the riverbank with magnificent views of the brightly lit skyline of Shanghai, and the food was amazing. But it seemed as if China wanted to make my trip especially memorable, and just as we finished our meal, a major firework display began on the other side of the river. We walked out to the riverside to watch it. Even the restaurant staff seemed surprised. On Monday, after packing, signing attendance certificates for both events, and having a quick lunch in the hotel, I left China and flew back to Los Angeles. It was an inspiring and memorable trip.

Essential oils and gut flora

In a blog post dated July 13th 2014, Madhupa Maypop quoted Paul Bergner, saying: “The scent of an essential oil can kill gut flora just like antibiotics do, according to Paul Bergner, director of the clinical studies program at the Rocky Mountain Center for Botanical Studies. He told me that breathing the oils puts them into the blood stream very quickly and can be a major disturber of intestinal health and contributor to poor immune functioning.” However this quote has now been removed from the post, since Paul Bergner has denied that he ever said this. Paul contacted me directly on July 15th, saying: “I have never said, or even thought, that inhaled essential oils could have any effect on the gut flora. There may be a theoretical concern about taking undiluted oils internally, but this has never been demonstrated.” The original Paul Bergner quote in fact comes from Susun Weed’s website. Paul has asked Susun to remove the misquote from her site.

It is true that inhalation of essential oils results in most constituents getting into the bloodstream (it’s not correct to speak of “essential oils” in the blood, since individual constituents are not equally absorbed). The same is true of any mode of application, though generally the amounts in the blood are in the range of 1-100 nanograms per mL of blood – quite low concentrations. Whether these constituents might then negatively affect the bowel flora is pure speculation.

Fit and slim female model exposing her belly and waist

We do know that enterically-coated capsules of peppermint oil are beneficial in cases of irritable bowel disease and that these capsules result in a (substantial) peak serum concentration of 1,492 ng/mL for menthol. We also know from this report that peppermint essential oil had a beneficial effect on the balance of gut bacteria in a case of SIBO (small intestine bacterial overgrowth).

It would be useful to know more about particular oils, doses, routes of administration and their effect on the body’s microbiome. But in the meantime, it is rash to assume that essential oils negatively affect the balance of bowel flora, because there is no clinical evidence that this happens. On the other hand, decades of clinical experience by doctors in France suggests that essential oils frequently heal both acute and chronic infections without the damaging, and often long-lasting effect on bowel flora that comes from the use of antibiotics.


EO Inhalation and Seizures?

Hi, I have a question regarding a possible adverse reaction to Young Living eucalyptus oil. A friend of mine was mopping her floor with some eucalyptus oil diluted in her mop water. The same day, her three year old had a seizure. He had never been diagnosed with a seizure disorder of any kind. He was taken to the ER and received several tests with inconclusive results. My friend did not make any connection between the oil and his seizure. About a week later, exactly the same series of events occurred. The second seizure lasted 24 minutes. She discarded the oil. Her son is still having seizures and was diagnosed with status epilepticus. He did not ingest the oil. The only routes of administration would have been diluted on bare feet or inhalation. Pure coincidence or a reaction with neurological damage?


Hi Amber,

Seizures are possible from essential oil inhalation, though rare. Seizures from eucalyptus oil are also very rare but do happen, and the younger the child the more susceptible they are to seizures. One case was reported in 2011 from a girl who used a head lice repellent lotion containing 11% eucalyptus oil. The same sequence of events happening does suggest a causal connection.

Best wishes,

Why Is Essential Oil Dilution Important?

dilutionHi Robert,
I’m having some trouble understanding my essential oil dilution research and was hoping you could clarify for me.

1.) Why is dilution so important if 95% of the oil evaporates when applying topically?

2.) Is dilution recommended due to sensitivities that could occur? I have used oils neat before and never had an issue.

Thank you for your time,

Hi Danielle,

It partly depends on why you are applying essential oils, and why to the skin. Much of my teaching is about cosmeceutical effects and products for skin care. Dilutions of essential oils are generally more effective in this area, because the skin does not respond well to concentrated EOs. They are drying, the risk of adverse reactions is increased significantly, and for skin care/personal care you simply do not need more than 1-5% essential oil.

About 5% of applied EO is absorbed into the body through the skin, but more if undiluted oils are used. When you first apply an EO to the skin, 100% of it is there for a while. This is when any adverse skin reaction will occur, so while it is true that most of it evaporates with time, this is not as relevant as the initial dilution.

Essential oil dilution is important for two safety reasons. One, to avoid skin reactions: irritation, sensitization and phototoxicity. Two, to avoid systemic toxicity, such as fetotoxicity, hepatotoxicity, carcinogenicity and neurotoxicity. Adverse skin reactions are obvious when they happen, but systemic toxicities may not be. Skin reactions are totally dilution-dependent, and safety guidelines exist to minimize risk. This does not mean of course that every time a person uses an undiluted oil there will be an adverse reaction. Many times there won’t. But more is not always better, and minimizing risk is generally a good idea. A phototoxic reaction for example, can be very, very nasty.

If you want to know more about what can go wrong and why, I would recommend my book Essential Oil Safety 2e.


Prague Report

RT in PragueIn 2013 I was invited to give a weekend presentation to the Czech Aromatherapy Association, and we set the dates for April 26/27 2014. On Thursday, April 24th I arrived at the airport in Prague, and was met by Jaromir and Blanka, who then took me on a one-hour drive around their beautiful city en route to the Hotel Step. Many of the existing structures date from the 14th century.

Friday was just for sightseeing on foot, and I was accompanied by Katerina Hroudova, Marie Noe and Hana Belikova. Hana would be my translator for the event. We saw some beautiful gardens with blooming lilacs, fragrant peonies and a Cedrus atlantica tree, and many statues, frescos and ancient walls, ending with perhaps the main tourist spot – the Charles Bridge. The coffee in Prague is excellent by the way.

How it turned out
Everything was set up perfectly on Saturday morning, and after some introductions I got started with my presentation, which was all about safety. This is a necessarily technical subject, and has the potential to be terminally boring, especially with translation slowing things down to half speed. But, there were three factors that made the weekend work.

One, I included some positive information about aromatherapy, all of which was relevant to the subject matter. When I talked about some in vitro testing that shows lavender oil to be cytotoxic to skin cells, I also showed evidence to the contrary, and illustrated the skin healing effects of lavender oil. This was part of a discussion on the relevance of in vitro testing. Two, the translation was excellent. At one point I said to Hana “you’re doing a great job” and she retorted “how do you know?” OK, I don’t understand any Czech, but when the translation is immediate, speedy and confident, it’s a very good sign. And, Hana is a professional translator, as well as being an aromatherapy enthusiast.

Three, the audience understood what I was saying! You can tell by facial expressions and body language, and also by the questions asked. I don’t just mean that the translation was effective, but that they understood the technical content and could see the connections I was making between constituents, oils, properties, hazard and risk. This suggests a thorough aromatherapy knowledge and training.

Seminar content
Clinical Safety, Prague Cz, Apr 2014The Saturday presentation included several slides showing different types of adverse reaction, the difference between hazard and risk, types of evidence, weight of evidence, inhalation, ingestion, transdermal absorption, and metabolism. Michal Babka, asked a question about dosage for animals, and I answered that this would be, as with humans, related to body weight. He mentioned that he had used essential oils to help a giraffe in the Berlin zoo.

On Sunday we talked about risks involving cancer, pregnancy, drug interactions and skin allergies. These subjects were not covered in their entirety, but examples were given illustrating key points. I also covered phototoxicity. This was not originally planned, but I realized early on that I needed a little extra material to fill the day. Following a question, there was a discussion about whether any fatty oils had any scientifically established SPFs. The outcome – probably not, because the existing research evidence does not meet regulatory standards.

When we got onto drug interactions, a pharmacist asked about whether grapefruit oil would interact with statins, cholesterol-lowering drugs, as grapefruit juice does. My answer was no, since the main compound in grapefruit juice responsible for drug interactions is not found in the essential oil.

Most of the audience was Czech of course, but there were also a few who had traveled just for the event, including Eva from Spain (who understood my English, but not the translation) a lady from Russia (who understood some English and some Czech) and a Greek lady who lives in Canada. I signed many books, including two of my older books written in Czech, and copies of the new Essential Oil Safety, which Marie, a publisher, was selling.

I was disappointed that Katerina Svoboda was not able to be there, but I was given a written note from her, which was a pleasant surprise. Katja has spent most of her career in essential oil research, and co-authored a book showcasing the kind of pictures of essential oil glands that illustrate the new Essential Oil Safety cover. We have known each other for many years.

On Monday April 28th, I made my way back to Ojai California with many new friends and pleasant memories.

Click here for the Czech language version of this content.
Klikněte zde pro české jazykové verze tohoto obsahu.

Australian Tea Tree Industry Insights

I spoke with Tony Larkman, CEO of the Australian Tea Tree Industry Association, about the nonprofit he heads, his own introduction to essential oils, and issues facing the essential oils industry and tea tree oil in particular.

Tony Larkman, ATTIA CEO

Tony Larkman, ATTIA CEO

Tony Larkman was born and raised in Kenya. After travelling extensively through Africa, Europe and the Middle East he returned to East Africa in 1986 to work first as a purchasing officer and then as a pig farmer before moving to Australia in 1992. Over the next 17 years Tony turned his hand to feed milling and grain trading before becoming an IT Manager and then a Purchasing Manager. In 2009 he started working for ATTIA Ltd where he realized that he had finally stumbled on the answer to a question that had plagued him since he was child: “What do you want to be when you grow up?” Tony is now the CEO of ATTIA Ltd which is probably the most organized and active industry body for any single essential oil.

RT: Your introduction to tea tree oil was as a pig farmer?
TL: It was the mid-1980s, and a spray bottle of ‘healing oil’ with tea tree oil as the active ingredient was hung near the door of every building on the piggery. We used it everywhere and for everything, for both workers and animals – from minor cuts and scratches through to cleaning and preparing wounds for stitching after fights between boars – some of which were horrendous and likely to have been fatal without the magic of the healing oil. It also helped mask some of the smell of a piggery, which was a bonus.

What is ATTIA, and what services does it provide?
The Australian Tea Tree Industry Association (ATTIA Ltd) is an Australian based not-for-profit organization formed in 1986 as the peak body to promote and represent the interests of the Australian tea tree industry. From the grower/producer to the manufacturer of off-the-shelf products for public use, ATTIA supports and promotes the responsible use of pure Australian tea tree oil (TTO). ATTIA’s aim is to develop a stable, cohesive, environmentally friendly, and internationally competitive TTO industry producing quality assured TTO that meets or exceeds international standards. ATTIA promotes the safe effective use of TTO for a wide range of applications. More information about ATTIA here.

Full membership of ATTIA is open to all Australian tea tree industry participants while associate membership is open to international participants in the supply chain. Our services include:

  • Support and advocacy in dealing with government and regulatory agencies, research and development groups and the media.
  • Leadership and representation in the formulation of overall industry strategy.
  • Generic industry promotion at national and international levels.
  • The collection and compilation of market data to inform all links in the supply chain of factors influencing supply and demand for pure Australian TTO.

Australian Tea Tree Industry Association

Is the ATTIA website useful for consumers, enthusiasts or practitioners?
ATTIA’s website was created to cater to all levels of interest from school children preparing a project through casual consumers and passionate enthusiasts to professionals. The most commonly accessed pages which are easily navigated to by using the drop-down boxes in the navigation pane at the top of every page are:

Home Page A summary of who ATTIA is and where pure Australian tea tree oil comes from.
About Tea Tree A more in-depth look at production, uses, safety and efficacy.
FAQ Answers 20 of the most commonly asked questions on tea tree oil.

For professionals and researchers there is also a regularly updated, searchable Literature Database where detail on more than 1,200 papers can be accessed. These include most articles published on the safety, efficacy and uses of pure tea tree oil since 1904 when the species from which pure tea tree oil is distilled (Melaleuca alternifolia) was first described by Maiden & Betche.

Australian Tea Tree harvest

Harvesting tea tree. Picture courtesy of Mark Webb

How much tea tree oil is produced annually in Australia and around the world and to where is it distributed?
We know that between 400 and 500 metric tons of pure Australian TTO is produced annually; this is dependent on the weather and growing conditions from year to year. 80% of this is exported, most to North America. In 2012 a total of 409 metric tons of Australian TTO was exported to the following destinations:

  • 50.27% North America (USA, Canada, Mexico)
  • 25.66% Europe (Continental Europe, UK, Russia)
  • 22.76% Asia (India, Middle East, South East Asia, China, Japan)
  • 0.98% Africa (South Africa, Egypt)
  • 0.33% South America (Brazil, Chile, Colombia)

Tea tree oil is also produced in several other countries including China, South Africa, Kenya, Indonesia and Thailand. All of this TTO is produced from Melaleuca alternifolia, an Australian native tree that originated in the coastal regions of Southern Queensland and Northern NSW. No one can accurately state how much TTO is produced in these other countries.

Are there different qualities of tea tree oil?
Let me clarify first that there is no ‘pharmaceutical grade’ of TTO, nor is there a ‘therapeutic grade’. These are purely marketing inventions intended to convince a buyer that a particular brand is in some way superior to that of competitors. The main ingredient and most active bacteriostat in TTO is terpinen-4-ol which, according to the current standard, must be between 30% and 48% in TTO. Almost all pure Australian TTO is traded today with 40%+ terpinen-4-ol. The only way to make sure you are getting the best available TTO is to ask the retailer or manufacturer if they are using pure Australian TTO and how they verify this. If they can’t (or won’t) answer then either they are cheating or they genuinely don’t know. If the latter is true please refer them to the ATTIA website or Facebook page.

The second great marketing myth that has been roundly debunked in scientific literature is the belief that the level of another compound invariably found in pure Australian TTO: 1,8-cineole, needs to be as low as possible to prevent irritation. Today’s standard allows up to 15% of 1,8-cineole (which is actually the main constituent of another Australian native essential oil – eucalyptus oil – which contains around 80% of 1,8-cineole, or eucalyptol as it is also known) and there is clear evidence  that it makes no difference in TTO at levels of up to 8%.

Pure Australian Tea Tree Oil

The ATTIA Code of Practice seal

Tea tree oil is steam distilled from the leaves and terminal branches of the Australian native tree Melaleuca alternifolia. When correctly distilled, stored and shipped any oil extracted from M. alternifolia is just as safe and efficacious whether it is produced in Australia or anywhere else in the world. In Australia all production, distillation, storage and shipment processes are stringently controlled through the ATTIA Code of Practice (COP) quality assurance program to guarantee that only pure, natural TTO derived from M. alternifolia is supplied in perfect condition to discerning manufacturers both locally and around the world. In other countries issues related to pesticide use, identification of source plants, poor distillation, as well as poor handling and storage practices can contaminate or degrade the oil to the point where it is no longer safe to use and cannot even be described as tea tree oil.

                                “TTO has an enviable reputation for its

                                antibacterial, antifungal, anti-inflammatory,

                                anticancer and antiviral properties”

In addition to these quality assurance issues, as TTO passes up the supply chain, some unscrupulous suppliers and traders deliberately contaminate it with byproducts that are derived either from other essential oils such as pine oil or from synthetic production processes. This adulteration can significantly compromise the safety and efficacy of the product when used as a replacement for pure TTO. In some instances I believe this practice has led to TTO being abandoned as a traditional herbal product because either ‘it doesn’t work’ or ‘it causes irritation’. The most frustrating part of this for ATTIA is that the claims made by those who sell the adulterated material are based in the main on ATTIA sponsored science into the safety, efficacy and uses of pure Australian TTO. More information on adulteration is available from a Facebook site, which was created specifically to raise awareness of adulteration in TTO.

These days pure Australian TTO is traded in commercial quantities using the International Standards Organization’s standard ISO 4730:2004 but the oil typically has 40% or more terpinen-4-ol, and a maximum of 3-4% 1,8-cineole, depending on the buyer. Occasionally you can still see “T39-C2”,”T39-C4” or “T40-C4” on some bottles; all they are doing is trying to differentiate their product from that of their competitors. The fact remains that there is clear scientific evidence that pure TTO is just as safe and effective regardless of the levels of terpinen-4-ol or 1,8-cineole as long as it conforms to ISO 4730:2004 standards. More information on the ISO standard for pure Australian TTO can be found here.

Tea tree quality standards

Tea tree quality standards

What are the principal issues that impact tea tree oil and essential oil quality?
I have already touched on adulteration as a major issue and I believe this is the most significant quality threat we currently face as an industry. However, even pure TTO can be degraded over time due to poor distillation, storage and handling so producers, traders, manufacturers and end users need to be aware of these factors and minimize their effect. Exposure to light, high temperatures and atmospheric oxygen all lead to degradation of some of the components of TTO which can increase the incidence of skin irritation and sensitization.

On the ATTIA website in the section about packaging you can find a paper on the stability of pure Australian TTO which can also be downloaded here. This details the science behind storage and handling procedures. A quick summary:

  • ATTIA recommends that pure Australian TTO sold to the public should only be stored in small (up to 100 ml) dark glass bottles at temperatures not exceeding 25oC with a use by date of 2 years from the date of manufacture in unopened bottles.
  • Once opened these bottles should be stored in cool, dark conditions with the cap tightly sealed and discarded after 6 months if still unused.
  • For bulk storage, the ATTIA Code of Practice requires producers to use only stainless steel storage and transport vessels and to store the oil in cool, dark conditions with minimum exposure to air.
  • ATTIA recommends 3 years from filling as the use-by date for pure Australian TTO sold in correctly filled, purged (Nitrogen or Argon) and tightly sealed stainless steel drums stored at an ambient temperature not exceeding 25oC.

What do you see as the outstanding benefits of tea tree oil?
TTO has an enviable reputation for its antibacterial, antifungal, anti-inflammatory, anticancer and antiviral properties, which are all well supported scientifically. In 2013, TTO was exported from Australia to 43 countries, where its uses include cosmetic, industrial, and medicinal applications. It is interesting occasionally to see that in advertising for some new or emerging essential oils, comparison is most often made to the efficacy and safety of Australian TTO – reinforcing its position as a global leader.

Australian TTO is a natural product that contains more than 113 compounds and I believe that it is the synergistic effect of these compounds that makes it a true healing oil. Some components like terpinen-4-ol (the major constituent of TTO) have proven antimicrobial and antifungal properties on their own but there are all the other components which must assist and complement the terpinen-4-ol with factors such as skin penetration, bactericidal, fungicidal and anti-inflammatory activity.

Another outstanding benefit is its proven ability to control commonly occurring bacteria such as MRSA and VRSA that are rapidly becoming totally resistant to all conventional antibiotics, particularly in hospital environments where management of these infections is proving such a challenge to healthcare professionals. I believe that as we run out of control options, more and more health professionals will turn to products like TTO that have not only proven antimicrobial activity but also possess a natural complexity that makes development of bacterial or fungal resistance extremely unlikely.

Flowering Tea Tree copy

Melaleuca alternifolia in flower

What current or upcoming research projects is ATTIA involved in?
Over the last 20 years the Australian tea tree industry has been fortunate to enjoy a close partnership with the Australian Government’s Rural Industries Research and Development Corporation (RIRDC). RIRDC has co-funded much of the research, development and extension work done to develop our industry through a tree breeding program, agronomy advances, development of distillation techniques and safe storage and handling procedures for pure Australian TTO. In addition to these basic but vital tools RIRDC has co-funded much of the University based research into the safety, efficacy and uses of TTO resulting in more than 50 publications which are available for download from the TTO page on the RIRDC website here.

Currently ATTIA is developing a test for adulterated oil which we hope to have adopted by internationally recognized standards organizations in the near future. Called the Chiral Purity Test, this measures the ratios of the optical isomers of three compounds that occur in pure Australian TTO: terpinen-4-ol, α-terpineol and limonene. Each one of these compounds occurs in two forms, with specific ratios in TTO. Since we know what these ratios should be, any variation is a strong indicator that the product has been contaminated. Table 1 below illustrates 57 samples of Australian TTO sourced directly from plantations over five years (2007 – 2011) showing a consistent ratio (70:30) of the two terpinen-4-ol enantiomers (dextro and levo). Table 2 shows 47 samples of commercially available TTO sourced from around the globe as well as a sample of 98% pure terpinen-4-ol. Some have a significant deviation from the expected ratio for pure TTO, indicating adulteration. This demonstrates how easy it is to identify real TTO from adulterated material. As well as synthetic terpinen-4-ol, potential contaminants include industrial waste from ‘normalising’ pine, eucalyptus and other essential oils. ATTIA intends to use the test to “out” any offenders by reporting them to the relevant regulatory bodies in their jurisdictions.

Chiral Ratios for Terpinen-4-ol

Table 1

Terpinen-4-ol enantiomeric %

Table 2

ATTIA is also keenly following the progress of researchers at the University of Western Australia (UWA) who are investigating the anti-cancer potential of pure Australian TTO. A few years ago topical application of a very specific formulation containing pure Australian TTO as the active ingredient was shown to significantly reduce the viability of melanoma and mesothelioma cancer cells in vitro and since then studies of skin cancers in mice have confirmed its ability to reduce or resolve some types of skin cancers. Researchers believe this may be due to the stimulatory effect TTO has on the body’s own immune system. Much work remains to be done before this reaches proof-of-concept stage.

Researchers at UWA are also investigating the clinical activity of formulated products containing TTO for activity against acne-causing bacteria. This will eventually result in a pilot study using volunteers to measure the activity of the most promising formulations in a human population.

For the grower members of ATTIA there is continuing support for research into high yielding genotypes of M alternifolia through both a conventional breeding program and using cutting-edge technology to identify specific gene markers for high yield and disease resistance that occur in natural populations. These markers can be used to quickly and efficiently identify individuals with outstanding properties from existing wild populations for infusion into the ongoing conventional breeding program to increase genetic diversity and ensure sustainability. In an emerging area ATTIA and the Australian Government have recently commenced a joint study to investigate the use of biochar generated from spent leaf and inter-crop legume planting to reduce both carbon and nitrous oxide emissions. Increasing productivity and developing a low emission industry not only ensures survival of an industry that utilizes a native crop plant in a sustainable way but also improves the green credentials of an already clean and green industry.

Tea tree oil safety issues that have been raised in the past include skin sensitization, endocrine disruption and bacterial resistance. What is your take on these?
I want to address these separately as all three are critically important questions and need different answers.

Allergic reactions and skin sensitization
TTO that has been well stored since distillation is a safe, natural product and its efficacy and safety is well known and documented. There is absolutely no doubt that some people are allergic to pure Australian TTO in the same way that some people are allergic to peanuts, milk or wheat. This can manifest itself in many forms from reddening, irritation and itching of the skin through to blisters and burns. Whenever and wherever TTO is used for the first time a user should make sure that it is diluted in a carrier oil (eg jojoba) to 10% before trying a small drop on the soft skin of the inside of the forearm. Wait 24 hours, unless immediate signs of itching or swelling are noticed. If a reaction occurs, immediately wash the area with soap and water and discontinue use. It is worth mentioning that slight, transient irritation is sometimes seen in clinical trials, this may be considered acceptable, depending on the benefits. However, allergic reactions are never acceptable.

Immediate, strong allergic reactions to TTO are uncommon and have been estimated to occur in less than 0.5% of the population. Sensitization to TTO has also been well documented; this occurs where repeated exposure to a product increases the reaction to its application. This can happen with pure TTO, but it is more likely to occur where TTO has either been poorly stored, which increases the level of peroxides and other irritants through oxidation, or when the oil has been adulterated.

Endocrine disruption
This is a myth and is the one that get me the most upset. I often see reference in scientific articles, blogs and online comments that refer to a link between gynecomastia (man boobs) and lavender and tea tree oils and I have been battling the negative publicity that erupted when the original work by Henley et al was first published in the NEJM in 2007. The authors linked the use of personal care products containing lavender and/or tea tree oil to breast development in 3 prepubertal boys and then went on to “demonstrate” that the endocrine disruption was caused by the two essential oils using well trays in the laboratory. These 96 well trays, made of plastic, contain phthalates which are known endocrine disruptors and I know from personal experience that TTO is an excellent solvent and extracts phthalates from any unprotected plastic it comes in contact with very quickly and efficiently. I believe this is why Henley et al reported the estrogenic and anti-androgenic “activity” of TTO and lavender possibly without even realizing the truth. More here.

RT-pub-lavender-2If you look at this another way, at least 400,000 kg of pure Australian TTO is shipped annually and used by thousands of people in hundreds (or even thousands) of products as well as being applied as an undiluted oil for medical, cosmetic and aromatherapy uses every day. If TTO did indeed have any kind of estrogenic or other endocrine disruptive activity then surely gynecomastia or at least some other symptoms would have been seen in more than the three boys Henley et al looked at.

Bacterial resistance
The suggestion that exposure to sub-lethal levels of TTO induced resistance in bacteria was first reported in 2007 and again in 2008 by McMahon et al. In 2008, and again in subsequent years, researchers at the UWA TTO research group tried to replicate the work done by McMahon et al to no avail. Repeated attempts by scientists at the University of Western Australia (Hammer et al 2008, Hammer et al 2012, Thomsen et al 2013) failed to induce resistance to any antibiotics in any of the bacteria studied and led them to conclude in 2013 that “…there is no evidence to suggest that tea tree oil induces resistance to antimicrobial agents.” Unlike most antibiotics, which are usually single molecules, TTO contains more than 113 naturally-occurring molecules. The synergistic effect of these compounds makes it improbable that bacteria could develop resistance to TTO.

Do you feel that current legislation impacting tea tree oil is reasonable, and do you anticipate more restrictive legislation?
We live in a world where regulation plays a major part in the registration and use of any cosmetic or medicinal ingredient whether natural or synthetic in origin. Regulations are there to protect users from harm. Some products and chemicals are very harmful if used incorrectly or indiscriminately so we all have to accept that regulation is a fact of life; ATTIA’s approach is and always will be cooperative. Having said that it is worth pointing out that legislation varies far too much around the world and I would prefer a more uniform approach to this in the same way that many countries are now adopting and moving towards the UN’s Globally Harmonized System of Classification and Labeling of Chemicals (GHS). This makes legislation far easier to manage.

Restrictive legislation is frustrating to any essential oil industry simply because most of it is designed to work with a single molecule which is clear-cut, easy to identify and assay, and is usually also patentable. An essential oil is a variable complex of molecules that, like the human genome, belongs to all of us and at the same time to none of us – in other words a regulator’s nightmare! However there is also no doubt that these oils are efficacious, safe and widely used around the world in cosmetic and medicinal formulations so I believe that regulators need to look closely at these naturally occurring substances and create separate legislation for them. This is beginning to occur in some places, but while these are being developed essential oil industries are being forced to address two separate sets of legislation, which can be burdensome.

What are the principal challenges facing the tea tree oil industry?
In the short to medium term adulteration of a pure, natural product with byproducts and other waste from chemical factories is the foremost challenge facing our industry today. This practice is motivated purely by profit and relies totally on the safety, efficacy and reputation of pure Australian TTO while undercutting the market price often to the point where a farmer cannot safely and sustainably produce the original product. The result of this cheating is to devalue TTO as a viable product. Unless it is combated vigorously, this could lead to adulterated or wholly synthetic concoctions becoming the norm for customers buying or trading ‘tea tree oil’ resulting in a devalued and virtually useless substitute for the real thing. ATTIA is currently cooperating with scientists and regulators from around the world to develop a cheap, effective test that will allow a discerning manufacturer to detect some of the more common forms of adulteration. Once this has been adopted by internationally accepted Standards organizations such as ISO and BP it will make it harder and far more expensive for those who adulterate pure TTO to continue to dupe manufacturers and end-users for their own gain.

Young plantation_ GD copy

A young tea tree plantation

In the longer term, regulation is the other major challenge. Any natural substance varies slightly from year to year and from region to region but there are recognized standards in place that  manage this so why can’t regulators also deal with the natural variation in these substances more sympathetically? On top of this there is also the prohibitive cost of developing data required in some jurisdictions to enable registration as a medicine or cosmetic ingredient. This can run into millions of dollars which cannot be recouped over the period a patent is usually granted for a conventional single molecule pharmaceutical because no patent is available for TTO. Traditional or customary use patterns covering many decades by bona fide practitioners should be acceptable evidence of the safety and efficacy of natural products such as TTO.

How does ATTIA help support the tea tree oil industry?
As an industry association, ATTIA provides both a forum and a vehicle for members (and non-members where necessary) to promote and act on emerging trends and regulatory, market or other pressures and trends in a timely and cohesive manner. By maintaining a monitoring watch on these factors ATTIA has been well placed to prepare and submit dossiers to regulatory bodies that include the USA, Canada and Europe. These submissions are prepared to ensure that pure Australian TTO can continue to be used in these jurisdictions both as a cosmetic ingredient and as a traditional herbal remedy for its wide range of clinically supported uses.

ATTIA also provides advice, training and auditing services in the critical area of quality assurance or QA. This promotion of ATTIA’s voluntary Code of Practice helps ensure that all pure Australian TTO offered into both international and local markets is always in perfect condition with documented QA practices that can be seamlessly incorporated into a manufacturer’s own QA procedures.

Since its inception ATTIA has also invested considerable time, effort and funding on research into the production, distillation, storage safety, efficacy and uses of pure Australian TTO. Much of this work, supported by ATTIA member donations and Australian Government Research and Development Grants, has been done at the University of Western Australia where the TTO Research Group has published more than 50 papers in their primary areas of research which are the antimicrobial and anticancer properties of TTO. Many of these articles are used to support claims and as proof of concept for the safety, efficacy and uses of pure Australian TTO. More on UWA here.

Estrogens in Plastic Labware

The safety of essential oils in puberty, and hormonal effects in general, are important health concerns. In a 2007 research report by Colorado and North Carolina doctors and scientists, in vitro evidence seemed to support the notion that lavender oil and tea tree oil were responsible for breast growth in three young boys, suggesting an estrogenic action. Although this article has subsequently been cited more than 180 times in scientific literature and is still widely quoted on medical websites, lavender oil has been exonerated and there is still no evidence of any link between the in vitro findings and the three cases. Now evidence is emerging that suggests the lab test results may have been due to estrogenic compounds in the plastic laboratory ware used.

In vitro: In an artificial environment, such as a test tube
In vivo: Occurring or carried out in the living organism

Plastic 96-well plate

Essential oils can leach estrogenic compounds from plastic trays like this 96-well plate.

In an April 2013 article the estrogenic claim is again made: “Other examples of naturally occurring endocrine disruptors include lavender oil, tea tree oil and fennel, all of which have been linked to breast development in prepubertal children presumably due to estrogenic effects.” (Note that ‘fennel’ refers to fennel tea, not the essential oil.) Christine Carson, Tony Larkman and myself wrote a letter contesting this assertion, and this is being published in the journal in March 2014. The important points of our letter are:

• Tea tree and lavender oils are now widely described as having estrogen-promoting properties.

• The research on which this assertion is based only demonstrated an in vitro effect.

• The plastic trays used in the in vitro testing contain estrogenic compounds such as phthalates.

• Essential oils are known to leach these compounds out of plastic.

• Therefore, the in vitro results could have been due to contamination.

• There is no other reason to believe that tea tree oil or lavender oil is estrogenic, and no estrogenic constituents of either oil has ever been identified.

• In vivo testing revealed no estrogenic action in lavender oil.

• No causal link was ever established between either of the essential oils and the three cases of prepubertal breast development cited by Henley et al.


Christine Carson is a microbiologist at the University of Western Australia

In our letter, Christine proposes that the in vitro results may be due to the essential oils leaching estrogenic chemicals, such as phthalates, out of the plastic containers used in the laboratory testing. Exactly this type of contamination of MCF-7 tests (such as those used by Henley et al 2007) has been demonstrated in plastic labware from 7 different manufacturers (Ishikawa et al 2001). This idea finds further support in a recent publication, which reported that frankincense oil began to dissolve plastic laboratory trays at concentrations of 50, 25 and 12.5% (Al-Kharousi et al 2013).

The idea that essential oils can affect the structural integrity of some plastics, beginning to break down, or dissolve them, is not controversial. Neither is the idea that plastic laboratory vessels can sometimes contaminate sensitive biological assays. Research from the University of Alberta describes how plastic laboratory products may be a likely source of error in many assays (McDonald et al 2008). The failure to appreciate the solvent properties of essential oils, combined with the use of plastic laboratory vessels, may have led to estrogenic activity being mistakenly ascribed to lavender oil and tea tree oil.

Only one other supporting study has been published (Nielsen 2008). The same type of laboratory plastic trays were used as in the Henley et al study (96-well plates), and the estrogenic action of tea tree oil was similar in both.

It is always unwise to assume that an effect seen from in vitro testing will also apply to the living body. There are many possible reasons for this, but the idea that the laboratory equipment itself might be affecting results is unusual.

Al-Kharousi ZS, Nzeako B, Mothershaw AS 2013 Initial observation on the interaction of frankincense oil with selected plastics. International Journal of Food Properties doi: 10.1080/10942912.2012.698442

Carson CF, Tisserand R, Larkman T 2014 Lack of evidence that essential oils affect puberty. Reproductive Toxicology In press

Fisher MM, Eugster EA 2013 What is in our environment that affects puberty? Reproductive Toxicology doi: 10.1016/j.reprotox.2013.03.012

Ishikawa T, Takano K, Fujita T et al 2001 Estrogenic impurites in labware. Nature Biotechnology 19:812

McDonald GR, Hudson AL, Dunn SM et al 2008 Bioactive contaminants leach from disposable laboratory plasticware. Science 322:917

Henley DV, Lipson N, Korach KS et al 2007 Prepubertal gynecomastia linked to lavender and tea tree oils. New England Journal of Medicine 356:479-85

Nielsen JB, 2008 What you see may not always be what you get – bioavailability and extrapolation from in vitro tests. Toxicology In Vitro 22:1038–1042

Politano VT, McGinty D, Lewis EM et al 2013 Uterotrophic assay of percutaneous lavender oil in immature female rats. International Journal of Toxicology doi: 10.1177/1091581812472209


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