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.
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.