Cats and essential oil safety

myrtle copy


I recently helped Vicki Rae Thorne with an article about cats and essential oil safety. You can find the article here, and it appears in the July 2011 edition of Animal Wellness Magazine. Vicki canvassed many opinions, and it’s an excellent piece, though I will say that I am not quite as concerned as it might appear. It’s true that cats are missing an enzyme (glucuronyl transferase) that humans do possess, and which is important in the metabolism of many essential oil constituents. Therefore, there is a theoretical risk of increased toxicity to cats.

Menthol, for example, is primarily metabolized (in humans and rodents) through glucuronidation, and toxicity testing shows that menthol is 3-4 times more toxic to a cat than a rat (Opdyke 1976). We don’t know for sure that the greater toxicity to felines is because of the missing enzyme, but it’s very likely. But, while 3-4 times is a significant difference, it’s not a massive one. I certainly don’t advocate dousing your cat in large quantities of neat essential oils – ever. And cats are quite susceptible to toxicity from nutmeg oil and tea tree oil. But, a small amount of any essential oil, and a moderate amount of most, will not harm your cat.

In 1995 a Japanese film crew came to my house in Brighton England, to film me and my cat Myrtle. It was for a Japanese tv show about famous people and their cats, but the focus was clearly on Myrtle, not me. And, I guess you did not have to be an A-list celeb to be classed as “famous” (though aromatherapy is more popular in Japan than in the US, and with my father-figure status…I’m just saying…)

The shoot with Myrtle was difficult. She was not a very social creature even with her family. At one point she hid under a bed, and my two (then little) girls decided to jump up and down on the bed, to “encourage” her to come out. The film crew’s focus went down to floor level in order to film Myrtle steadfastly staying where she was, with the mattress bouncing up and down on her head. This went on for some time.

Somehow Myrtle survived a further 13 years and when she passed away she was replaced by Ziggy. Ziggy is a Maine Coon, a breed of cat ideally suited to cold climates. Maine Coons have long hair, even between their toes, and long, bushy tails. So, not exactly perfect for Southern California weather, but when we got him as a kitten he didn’t look especially hairy! I have never used essential oils on Ziggy, because I have never had a reason to. I did use tea tree oil on Myrtle once, when she had an infected puncture wound. I squeezed out the pus, and dripped one drop of tea tree oil into the hole. I repeated this treatment over next two days, and she healed up fine after that.



However, an “overdose” of tea tree oil could be lethal to a cat. A total of 60 mL of undiluted tea tree oil was applied to the skin of three cats, as a treatment for severe flea bites (the cats had previously been shaved but there were no nicks) and to prevent further infestation. Later the same day, one cat was hypothermic, uncoordinated and unable to stand; one was comatose with severe hypothermia and dehydration, and one was trembling and unsteady. After intensive treatment two of the cats recovered and one died (Bischoff and Guale 1998).

The outcome is perhaps not surprising considering the very large amount of essential oil used, 20 mL on each cat. Given that a typical cat weighs 3-5 kg, this is equivalent to 4.0 – 6.6 mL/kg, although not all of it would be absorbed. The cat that died had elevated liver enzymes, suggesting hepatotoxicity. Several cases of toxicosis have been reported when tea tree oil was applied dermally to dogs and cats. In most incidents the oil was used to treat skin conditions at inappropriate high doses. The typical signs observed were depression, weakness, incoordination and muscle tremors. Treatment of clinical signs and supportive care has been sufficient to achieve complete recovery within 2-3 days (Villar et al 1994). But perhaps the greatest aromatherapy-related threat to a cat’s health comes from pennyroyal oil. On the NOW Foods website you will find the following:

“Fun fact: Back in the days of yore, pennyroyal was also known as “pudding grass” for its use in a stuffing made of pennyroyal, honey, and pepper that was often used in hog’s pudding. Pennyroyal is a member of the mint family, and exudes a fresh, minty, herbaceous scent. While its scent is actually a bit more powerful than other mints, its therapeutic value is actually not as strong. Pennyroyal was used frequently by Ancients for a variety of ailments, and remains current in the British Herbal Pharmacopoeia, which recommends it for flatulence, intestinal colic, the common cold, delayed menstruation, and gout. However, its primary use in today’s world of aromatherapy is in pet care. Pennyroyal was a favorite of Pliny the Elder in the fight against fleas, and remains a favorite natural enemy of fleas to this day.”

The back label of NOW pennyroyal oil

The back label of NOW pennyroyal oil

Here’s another fun fact – using undiluted pennyroyal oil to treat your cat’s fleas could also kill your cat. We know that pennyroyal oil is toxic to the liver in both rodents and humans. We don’t know about toxicity to cats, but it can’t be any less toxic. Many websites do contain warnings about pennyroyal oil, and using dried, crushed pennyroyal leaves is perfectly safe. However, the fact that you can buy a 1 oz bottle of pennyroyal oil, and that neither it (see left), nor the above (related) website specifically tell you (a) not to use pennyroyal oil undiluted on your pet, nor (b) how much to dilute it for it to be safe, is worrying. (The reference to “aromatherapy” on the label is intriguing – what constitutes “aromatherapy use”? I certainly can’t think of a scenario in which undiluted pennyroyal oil would be safe.)

The rat oral LD50 value for pennyroyal oil is 400 mg/kg (Opdyke 1974) compared to 1,900 mg/kg for tea tree oil (Ford et al 1988) so pennyroyal is approximately 4.75 times more toxic than tea tree. Since 20 mL of dermally applied tea tree oil is lethal to a cat, then the probable equivalent lethal dose of pennyroyal would be 4.2 mL. I have little doubt that, in sufficient concentration, both essential oils will kill fleas, but there has been no published research on essential oils and cat fleas, dog fleas or human fleas. So we really don’t know what would be a toxic concentration to fleas, while being nontoxic to cats. My advice – tea tree oil is fine to use at up to 5% on cats, and pennyroyal at up to 1%. Whether these concentrations would repel or kill fleas I have no idea, but I would suggest not using pennyroyal oil as a pet flea treatment. Sensibly used, most essential oils are safe to use in pet grooming products.

Bischoff K, Guale F 1998 Australian tea tree (Melaleuca alternifolia) oil poisoning in three purebred cats. Journal of Veterinary Diagnostic Investigation 10:208-210

Ford RA, Letizia C, Api AM 1988 Monographs on fragrance raw materials. Food & Chemical Toxicology 26 supplement, p407

Opdyke DLJ 1974 Monographs on fragrance raw materials. Food & Cosmetics Toxicology 12 supplement, p949-950

Opdyke DLJ 1976 Monographs on fragrance raw materials. Food & Cosmetics Toxicology 14 supplement, p471-472

Villar D, Knight MJ, Hansen SR et al 1994 Toxicity of Melaleuca oil and related essential oils applied topically on dogs and cats. Veterinary & Human Toxicology 36:139-142

60 comments to Cats and essential oil safety

  • robert

    Hi Mark,

    Since the tea tree oil was diluted it’s probably fine anyway, and since you washed it off, definitely no problem.

  • Ryry

    I used citrus oil on my cat after a bath because he has fleas. It was diluted but I didn’t know cats couldn’t have citrus oil…something in my gut told me I should look into it right after I did it and I found out it was toxic! So 5 minutes later I have my cat 2 baths just to be sure I washed it all off but I don’t know how much he had licked off his fur in those minutes. He seems to be acting fairly normal but should I be worried?

  • robert

    Ryry, I think your cat will be absolutely fine. I don’t know how much you used, but citrus is not especially toxic to cats, and if you washed it all off, no problem!

  • Niqi

    Whenever my cat gets an eye infection I bathe her eye with a dilution of tea tree oil. I use 1 to 2 drops of tea tree oil in a small bowl of luke warm water, which I mix vigorously with my fingers and then with cotton wool I gently clean her eye area letting the water run into her eye. I usually do this twice a day and she is perfectly fine afterwards and usually by day 2 or 3 at the most her eye is better.

    Lately part of my cats gums were very inflamed looking and her breath has become very smelly. So I have been putting 1 drop of tea tree on the end of my finger and rubbing it onto that part of the gums, …well trying to anyway, it usually lands up somewhere in the mouth. She of course hates it but is otherwise fine. I been doing this once a day over 3 days and then having a few days break and then doing it again over another 3 days etc. She is 12 years old and very healthy except for the abovementioned problems.

    However now I have come across a lot of sites on the internet saying how toxic tea tree is to cats and that surprises me as that has not been my experience as long as the essential oil is diluted or in very small doses.

    I will carry on cleaning her eyes with tea tree if she gets an infection as it works wonderfully as apposed to the chemical ointment the vet gives you which doesn’t work half as effectively.
    I’ll err on the side of caution and stop applying it to her gums as I’m afraid that it could build up in her system as some of these sites seem to suggest.

    Also if I can put tea tree in my cats mouth and there is no adverse reaction except dislike, then maybe the other chemical ingredients in these pet shampoos and products etc should be investigated.

  • michele

    I had a cat who had reactions to flea powder at one point, and unfortunately a not so easy case to cure fleas. We used 5cc of pennyroyal in 4 oz of baby shampoo mix to shampoo the cat. that makes it in theory less than 5% solution if it was directly applied, which it wasn’t. once it was foamed up, we only used about 2 teaspoons total if that, the fleas jumped off into the water. i’m sure there was some residual left on the kitty, but likely little. we only had to give him about 2 baths to rid him of fleas. seemed none the worse for wear. I would likely use an even more dilute solution next time.

  • robert

    Hi Niqi, thank you for your comment. Your eye preparation is slightly risky, as the oil will not properly dissolve in the water, but it sounds like you’re making sure it’s dispersed as well as possible before using. One drop of tea tree oil in your cat’s mouth per day for 3 days – well, if your cat swallows all of that essential oil then it’s a significant amount. You could probably continue with this if the oil was diluted to 10% and then you applied one drop of that.

  • robert

    Hi Michele – to be honest, this is risky. 5 cc (5 ml) of pennyroyal oil would be more than a fatal dose for a cat if it was ingested. In one case, 30 ml was fatal for an adult human when ingested, and 60 ml killed a dog that weighed 30 kg when applied to the skin undiluted. I appreciate that you are mixing into shampoo at 5%, and not even using all of it. And, your cat survived, so clearly this was not fatal, but pennyroyal is specifically toxic to the liver. Yes, it is toxic to fleas, but be careful with your cat!

  • Victoria


    Perhaps the inflamed gums and bad breath are related to administering Tea Tree Oil – internal organ damage can manifest as bad breath, amonsgt other symptoms. To be on the safe side, always get a diagnosis from your vet before administering any treatment.

    Hope this helps.

  • Hi Robert, I appreciate you adding a common sense angle to the cat essential oils discussion, it is true that at the dangers of essential oils are greatly over-exaggerated. On the other hand, essential oils do kill cats when used improperly, and the dosages you are suggesting are high. I am contacted more often than I like by people who have applied undiluted eucalyptus or tea tree, or YL purification to their cats and the cat has become lethargic/comatose or is showing neurological symptoms, drooling and uncoordinated, several of these cases have been fatal. I encourage people to use hydrosols for cats, it is safer and more pleasant for the cat. Also, essential oils are not a very effective flea repellent (rapid dissipation), diatomaceous earth and neem oil are much better options.

  • Olivia

    Maybe the cat with the inflamed gums and stinky breath needs a teeth cleaning at the vet. At any rate the cat’s mouth should be checked out by your vet. One of my kitties passed away from a cancerous tumor of the gums…it developed rapidly.

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