ESSENTIAL OILS: THEIR LACK OF SKIN ABSORPTION, BUT EFFECTIVENESS VIA INHALATION.

  By Martin Watt

PREFACE: I am anxious that people do not misconstrue my articles as indicating that I don't think aromatherapy works. This is far from the truth as I whole-heartedly agree the therapy can have wonderful healing benefits. However, I am certain some of the traditionally held views on how it works are misleading. I am fighting to prevent a wonderful therapy from being turned into a pseudo-religion by some of the 'gods and goddesses' in the trade. This will lose aromatherapy credibility particularly within the medical profession where it can have huge benefits.

Some people teach what the audience 'wants to hear' as well as pandering to 'spirituality' as a way of covering up their own lack of appropriate knowledge. It is also clear that an awful amount of research from the sciences associated with the use of essential oils, has become corrupted when it has crept into aromatherapy books and training courses. It has become clear to me that many authors and course providers simply have not studied their trade as thoroughly as they should have, before embarking on passing on their knowledge to others.

Aromatherapy can be a potent therapeutic tool for unlocking the brains inhibition of normal bodily processes due to various emotional factors. It is excellent for giving relief from many musculo-skeletal ailments. Essential oils can achieve spectacular results when treating various kinds of skin trauma. However, much confusion and misinformation exists about two relatively
separate forms of treatment: (1) massage. (2) the use of aromatic oils with or without massage.

History:

Various types of plant oils and fragrances have been used since ancient times as external applications for wounds and skin conditions. Most aromatic oils used prior to about 1600 AD were not distilled, but were produced by macerating plants in hot vegetable oils or more commonly in animal fats. The resulting product could contain a similar amount of essential oil to that found in a modern diluted massage oil. A vital point to remember, is that macerated or infused oils, would have contained numerous natural plant chemicals that do not appear in a modern distilled oil. In a few cases these 'other' plant constituents may be advantageous, aiding the therapeutic actions of the infused oil. However, in several cases the extract would contain disadvantageous skin irritants, sensitisers and viable fungal spores.

Therapeutic activity:

Some of the aromatic 'essential' oils used in aromatherapy do have well-documented therapeutic actions. However many of the oils for which aromatherapists claim physiological medical activity, in fact possess no recorded historical medicinal actions. Oils such as Moroccan chamomile, Citronella, Clary sage, Geranium, Rosewood, Vetiver and Ylang were originally produced solely for the perfumery and fragrance trades. Certain oils such as aniseed, cubeb, dill, fennel, peppermint, sandalwood, etc. have been used over several hundred years for a variety of ailments. However such oils have mainly been used internally as medicinal agents. The vast majority of reports about their therapeutic activity come from ORAL consumption.

It is very common in aromatherapy books, to find that the writer has taken the documented actions of the herbal extract, and applied this directly to the essential oil yielded by that same plant. It is totally incorrect to assume that because a HERBAL extract, given by mouth has a known medicinal action, that any essential oil distilled from it will possess the same or even similar actions.

Many of the essential oils for which aromatherapists claim explicit physiological effects such as: "Fennel is diuretic,"  "Geranium regulates the hormonal system," "grapefruit is good for cellulite." Cannot be demonstrated to have direct physiological actions when these oils are applied to the skin during massage.
Fennel for instance is well known for producing an increase in urine output when it is consumed as a medicine. However when the volume of essential oil used in the average massage is applied, it is very doubtful that enough essential oil can be absorbed through the skin to elicit any diuretic action. If very large amounts are used, the skin is occluded (such as with compresses), or the essential oil is used in hot humid environments, then I am prepared to accept a fair amount of oil gets into the subcutaneous tissues. Diuresis however, has, in fact, been proven to occur following ordinary massage without the use of any essential oils.¹

I believe the major modes of action of essential oils used in aromatherapy are:

1. The psychotherapeutic effects of the oils on the olfactory system and the brain.
2. The absorption into the circulation of some of the oils constituent chemicals via the nasal membranes and lungs.
3. For muscular problems, if very much higher percentages of essential oil than are normally used in massage are 'rubbed in' or applied on compresses.
4. Damaged skin can often benefit from using 'healing' essential and fixed oils. This form of treatment may not be strictly 'aromatherapy', but it is closely allied. This is because the essential oils can have a direct pharmacological action on damaged tissues, as well indirect beneficial effects on the mind if the aroma is pleasant.

The effects of essential oils on the brain via the olfactory system.

This is the basis on which the perfumery trade functions, and is the way I believe most aromatherapy works. The fragrance trades have sponsored substantial research on the psychological effects of aromatic substances. It has been clearly demonstrated in animals and humans that the brain wave patterns are affected to quite a remarkable degree when aromatic vapours are inhaled. It has even been shown that brain wave patterns are altered, when human subjects inhaled aromatic vapours at such a low level that they said "they could not smell the substance that was being administered." This experiment in particular, clearly demonstrates that the human sense of smell is much more acute than it is normally credited with. Perfume manufacturers have based their business around the effects that certain perfumes can have on the emotional state of both the wearer and people they come into contact with. Therefore, a whole business, that world-wide is worth billions of dollars is largely based on the psychological and emotional effects of fragrance. It is therefore somewhat peculiar that this most important aspect of the use of fragrant plant oils, is not the linchpin of aromatherapy. Rather most courses insist on dogmatically sticking to the hypothesis that the oils achieve a pharmacological effect by being absorbed through the skin and into the circulation.

Skin absorption of essential oils.

I remain extremely sceptical that this is a route by which significant volumes of most essential oils can enter the body. After years of looking at so called 'scientific' research, I have failed to find one trial where the methodology used has been adequate, including the paper on Lavender absorption published by Buchbauer et al.² When I spoke to Dr. Buchbauer in New York, he said that "no precautions were taken with the subject on whom the Lavender oil was trialed, to prevent the inhalation of the volatile molecules." This is the critically important area that I have found time and time again being overlooked by researchers. They always fail to understand the fundamental nature of most essential oils, which is that they are extremely volatile substances. As such they quickly find their way into the respiratory tract epithelium and thence to the bloodstream.

Currently a lot of theoretical skin biology is being taught in aromatherapy courses. Most tuition is based on theoretical models of how essential oils may be metabolised once they have gained access to the layers of skin where enzymatic reactions are known to occur. As a small number of drugs are now administered in the form of skin patches, this is promoted as being 'conclusive evidence' that essential oils are freely absorbed in a similar manner. Yet even hormone patches require the solution of the hormones in ethyl alcohol in order to permit their absorption by the skin.

Scientific references supplied by various authors about 'evidence of skin absorption' frequently refer to experiments of little relevance to aromatherapy such as:

1. Individual fragrance chemicals (usually synthetic) are used-not the WHOLE oil with its hundreds of different chemicals.³

2. The substance being tested has often been applied under occlusion (covered),⁴ which does force the substance into the skin. However this ignores the fact that when essential oils are used in massage, body heat will quickly evaporate the vast majority of the highly volatile chemicals away from the skin, thus permitting quick inhalation. The use of a vegetable carrier oil probably makes little difference to the amount of essential oil absorbed by the skin. This is because the volatile chemicals in essential oils evaporate within seconds of application to a warm area. Also the rate of evaporation from the skin is likely to be substantially enhanced by the heat generated by the massage. Again, I have to remind you that even when using carrier oils, you can quickly smell the essential oils used. The mere fact that you can smell them means the vapours are gaining immediate access to the respiratory tract.

3. Of Major importance, is the most fundamental error of all research that I have come across-no precautions have been taken to prevent inhalation of the essential oil vapours. I have read all of the paper published by Rommelt et al. in 1974 ⁵ although I have not seen subsequent work done by that team. However in the oft quoted 1974 paper, aromatherapy writers and some scientists, simply overlook the fact that 150 ml. of pine oil was added to the bath of the subject, and no mention was made of how he breathed. It does not surprise me that he excreted α-β-pinene and camphene for several days. How on earth can anyone compare the effects of 150 mls. with the few drops of essential oils used in the average massage. The same researchers indicated there may be some absorption of essential oils from ointments. Indeed there may be a little absorption by this method, but I do not know if the inhalation factor was excluded in any trials. Ointments have an extremely ancient history of being used as local applications for musculo-skeletal problems, but there is little sound data suggesting that the volume of essential oils, so absorbed, can have anything other than a localised effect.

I am not aware of any evidence suggesting that enough essential oil is left in the bloodstream to have any effects on other organs, has anyone out there got any irrefutable evidence? Until experiments are conducted with the people being massaged having an air supply under pressure and from a remote source, then all these tests are unreliable. Interestingly no one in complementary medicine seems interested in sponsoring such a simple trial, I wonder why?

4. In fact, there is far more evidence to support the opposing view, that most essential oils are NOT FREELY ABSORBED. Human skin seems to more readily permit the absorption of a number of water soluble plant chemicals such as the nicotine anti-smoking patches, nicotine being a water soluble alkaloid. Many national pharmacopoeias contain formulations for lotions, creams and ointments for painful conditions such as sciatica, neuralgia & arthritis based on water soluble plant alkaloids.
There is, however little evidence to support the theory that human skin will readily permit the passage of the lipid (fat) soluble portions of plants (barring a few exceptions). In traditional medicine we find few examples of plant oils being used for anything other than localised treatments. Fixed and volatile plant oils have always been used principally for cosmetic and skin care purposes.

Of utmost importance, is not if essential oils are absorbed into the superficial dead layers of the skin, as clearly this does occur. But, does sufficient find its way into the body via the skin to have any clinical effects? My investigations of dermatological literature have led me to the following conclusion: When a few natural chemicals in essential oils are absorbed by the skin, with a few exceptions, it is found that those same essential oils are well documented as causing adverse dermal and systemic reactions. This seems to me to indicate that many essential oils are alien to the immune system when they are taken into the body via the skin.

I offer the following evidence on skin absorption or the lack of it. The monographs published by the R.I.F.M. provide the following unless indicated. There is insufficient space to give full references, but they are available in those monographs. I must add here, that even where absorption of volatile chemicals has been indicated, without exclusion of the inhalation factor the results must still remain questionable.
 

CHEMICALS (frequently not natural but synthetic)

ABSORBED through the skin of animals. NOTE: human skin is far less permeable than animal skin. Benzyl acetate, benzoic acid, camphor, d-carvone, cinnamic acid, coumarin, para- cymene, d-limonene, methyl salicylate, α-phellandrene, terpineol, (α-β-pinene & camphene at 150 ml. see para. 3). d-limonene; only 3% was absorbed in vitro across isolated human skin, while in rats the figure was 6%.⁶ AUTHORS NOTE: One probably gets higher levels of d-limonene in the blood from eating orange flavoured drinks, sweets, cakes, liqueurs, etc.

NOT ABSORBED: linalool within 2 hours of application.⁷ d-pulegone in pennyroyal, carvacrol in some thymes and mints, eugenol, isoeugenol & methyl benzoate in clove, tuberose and ylang, fenchone in anise, fennel & some lavenders, geraniol in geranium & palmarosa. Those chemicals in extra bold are considered by some to be the "active" components in our most important essential oils. I do not agree that this is the case, as I consider them to be just a part of the package of chemicals that give essential oils their properties.

Evening primrose (fixed oil) not absorbed through the highly permeable skin of premature babies, but it was thought that water and oil emulsions (creams or lotions) may be more favourably absorbed.⁸

WHOLE ESSENTIAL OILS TESTED FOR ABSORPTION

ABSORBED: cumin, tansy.

NOT ABSORBED: Lavender (see ref. above on linalool), tolu balsam oil, copaiba balsam oil, parsley seed, patchouli, pimenta berry and leaf.

The systemic absorption of aromatic molecules via the nasal passages and lungs.

  This method by which aromatic molecules in essential oils gain access to the body has been demonstrated. When Rosemary oil vapours were introduced into the atmosphere of caged mice, it was shown that blood samples contained a substantial proportion of one of the chemicals present in the inhaled essential oil. This proved the volatile chemicals in essential oils, can gain access to the bloodstream in significant amounts, if the concentration in the atmosphere is at an appreciable level.9

UPDATE:

Since the time of writing, trials on humans have confirmed that indeed, significant volume of essential oils do gain access to the blood via the respiratory tract. As the brain is a 'blood hungry' organ then clearly the first port of call for aromatic molecules absorbed via the olfactory epithelium is likely to be the brain. It is of course, well known that certain drugs are known to act extremely quickly when they are sniffed up the nose.

CONCLUSION:

I believe it is likely that we get a complexity of effects when essential oils are inhaled:

1) A direct pharmacological effect via the blood supply to the brain.
2) An indirect effect via the olfactory nerve pathways to the brain.
3) The beneficial effects from the massage and the touch receptors.
4) The good old powerful placebo effect, caused by client therapist interactions.
5) Possibly a regulation of energy flows via similar pathways to accupressure/acupuncture.

With that kind of bombardment, it's not surprising that aromatherapy can achieve such excellent results. The therapy clearly is potent at reducing the brains inhibition of the body, from carrying out its routine regulating and healing activities.

References:

1. E. Ernst M.D. et al. 1987, Physiotherapy vol. 73, no. 1.
2. J. Buchbauer et al. Jan-Feb. 1992. J. of Am. Soc. of Cosmetic Chemists, 43; 49-54.
3. Bronaugh et al. 1990. Fd. & Chem. Tox. 28, (5), 369-373.
4. Hotchkiss et al. 1992. Fd. & Chem. Tox. 28, (6), 443-447.
5. H. Rommelt et al. 1974. Munch. Med. Wschr. 116, 537.
6. S. Hotchkiss, St.Mary's Hospital, London. Published; New Scientist, Jan 1994, p.24-27.
7. Meyer & Meyer 1959, Arzneimittel-forsh 9,516.
8. E.J.Lee et al. Arch. Dis. in Childhood 1993,68: 27-28.
9. K. Kovar et al. 1987. Planta Medica 53, 315-318.

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