Dermal Absorption of Essential Oils
Like most aromatherapists, I was taught that
essential oils penetrate the stratum corneum via the skin surface and then pass through the dermis, entering the general circulation. This is accepted as being the most important route for essential oils to work in aromatherapy and a full body massage is the usual way aromatherapy is administered, although the oils are also used in lotions, creams and other carrier media, compresses and baths for dermal absorption. Where a full body massage is not possible, a back massage is indicated because “the back presents the single largest expanse of skin of any body area” (Davis 1988 pp.218). According to Gattefossé (1937 p.62), who is considered to be the “Father of aromatherapy” as he coined the term ‘aromathérapie’, cutaneous absorption of volatile substances has been demonstrated physiologically and clinically and is better if the product is brought to body temperature. However, he did recommend that the skin is cleansed first with a solvent and that the substance is not too volatile as to dissipate into the air. It must also dissolve fats rapidly and he suggested they be dissolved in alcohol. Some drugs are now administered in the form of skin patches, and this is taught as being "conclusive evidence" that essential oils are freely absorbed in a similar manner; however according to Watt (1993) “even hormone patches require the solution of the hormones in alcohol or other solvents in order to permit their absorption by the skin”. Valnet (1980) on the other hand gives that, “The skin’s absorptiveness has always been exploited in the treatment of general conditions (e.g. with iodine paint or friction rubbing with liniments based on garlic, olive oil or camphor). The modern pharmacopoeia contains many ointments whose active principle (anti-coagulant or hormonal), is designed to have an effect on the whole body through rubbing on the skin” (Valnet (1980) p71). The “Mother of Aromatherapy” is a title affectionately given to Madame Marguerite Maury and in her book “Guide to Aromatherapy ”, first published in French in 1961 (p71), she surmised that essential oils penetrate the bloodstream via the capillaries and cites Dr Badmadjeff as the source of this information. It is through her research that we use massage in aromatherapy today as she had originally given her clients essences to inhale yet had found this to be a temporary and unsatisfactory form of treatment. Robert Tisserand explores Mme Maury’s work (1980 p71) and explains that cutaneous penetration of essences is slower, more diffuse and therefore safer than inhaling or indeed ingesting them. In the UK, aromatherapists do not administer essential oils internally as only a medically trained herbalist has the knowledge and training to prescribe this safely. All our work is done through cutaneous absorption and inhalation and it is sometimes proffered that internal ingestion means that essential oils are altered by chemical digestion/enzymes. However, Burfield T (2004) also states that metabolic changes of
absorbed essential oil components by enzymes within the dermis, may frequently occur. Another key figure in aromatherapy teachings, Dr. Jean Valnet, confirms that research existed at the time of writing his book that proved essences pass through the layers of skin to be rapidly circulated in the blood and eliminated by the lungs and kidneys. He cites studies carried out by Valette C. (1945) where oils
were used on rabbits (Valnet. (1980 p69). However, according to Watt (1993), “human skin is far less permeable than animal skin” and so this may not be an accurate representation of what occurs in aromatherapy on humans.
It follows that all the books written subsequently on aromatherapy have remained faithful to what has been written before and have published that essential oils are readily absorbed through the skin (P Davis 1988 p9, Ryman D. 1984 p 41, Lawless J. 1992 p.26, Price S. 1993 p8 etc.). Websites also follow suit with statements such as “Many essential oils are lipophilic, meaning that by their molecular design they want to jump into tissues containing protein, like our skin” (Bioexcel n.d.). Price cites Gattefossé’s research on absorption taking between thirty minutes to twelve hours to be totally absorbed after rubbing on the skin, confirmed by another researcher Schilcher, (1984). In addition, Vickers (1997 pp.143-144) gives useful evidence confirming dermal absorption. Vickers. also says in his book that most aromatherapy books are written for the lay person and certainly this is true for a large amount of the literature available to the aromatherapy student. Most do not check the sources of their information and those that do often do not support the claims being made (Vickers 1997 p.64).
So why does there exist this extreme controversy about dermal absorption of essential oils?
Surely, this is not helping the aromatherapy profession to become a credible source of healthcare as we all want it to be. With regulation of the profession we need to have conclusive proof of what we say aromatherapy does and solidarity if we are to work alongside mainstream healthcare providers and continue the growing trend of integrated medicine. Massage is only one way of
using essential oils but all the topical applications rely on essential oils penetrating the skin and entering the blood. The other way volatile essential oils enter the bloodstream is through the respiratory tract and this is where some of the dermal absorption research goes wrong. As constantly argued by Watt,
much of the research fails to make adequate precautions to prevent inhalation of the essential oil vapours. Therefore, of course essential oil molecules will be found in the blood due to inhalation and this does not prove dermal absorption occurs conclusively.
In an article by Ron Guba (2002) it is confirmed that essential oils are absorbed by the skin, but states that “with topical applications, we cannot assume full absorption of applied essential oils. If we do not occlude (or cover) the site of application, as is generally the case with topical aromatherapy applications, the dose is significantly lessened by evaporation. It is clear that topically applied essential oils will penetrate the epidermis of the skin”. One American study found that 75% of an applied dose of various fragrance compounds was absorbed through human skin when the skin was covered after application. When the skin was left uncovered, the total amount absorbed dropped to only 4.0% (Battaglia 1995 p136). It seems prudent therefore that all aromatherapists should cover the area just massaged and where blends in carrier media have been applied, with warm towels or blankets. This would actually be a lovely way of relaxing, covered in warm blankets after or even during an aromatherapy treatment. However, it is an area that still requires further research to understand how a variety of different factors (such as the type of essential oil compounds, the recipient or "carrier" base used, temperature, etc.) affect the amount absorbed through the skin (Guba 2002). I have experimented myself with Lavender oil and groups of students over the years by dabbing a drop of neat lavender (Lavandula angustifolia) on the external cheek and seeing how long it takes before they can taste the lavender oil on their tongue. Most taste it quickly, some take longer and usually one or two in a class taste nothing at all. This proves some absorption through the skin and also the difference in absorption rates from person to person. This is confirmed by the EUROPEAN COMMISSION: EVALUATIONS AND PREDICTIONS OF DERMAL ABSORPTION OF TOXIC CHEMICALS January 2001- February 2004 that states” Also skin thickness will need to be considered”.
I received details of research on dermal absorption from Robert Tisserand to help answer a query on this subject received in the Aromatherapy Consortium office back in 2004: In a human study, peak plasma concentrations of two Lavender oil constituents were detected 20 minutes after the oil had been applied by massage; after 90 minutes, concentrations had fallen close to zero (Jäger et al., 1992). In this study 1.5 g of massage oil (2% Lavender oil in Peanut oil) was gently massaged over the abdomen for 10 minutes, and blood samples were drawn from the arm 0, 5, 10, 20, 30, 45, 60, 75, and 90 minutes after finishing the massage. The two components measured were linalool (24.8% of the oil) and linalyl acetate (29.6% of the oil). Linalool peaked at 120 ng/ml plasma after 20 minutes.
As argued above by Watt (1993) the Jäger et al study does not appear to have controlled for inhalation and pulmonary absorption of the essential oil. However, earlier work by Schuster et al (1986) did ensure that subjects inhaled “clean” air, and plasma concentrations of ãpinene, βpinene, camphor, 3-carene and limonene were determined over a period of 3 hours. Pinimenthol ointment (2 g) was applied over a 400 cm2 area of skin in 12 human subjects, and plasma levels peaked at between 1 (camphor) and 10 (ãpinene) ng/ml plasma after 10 minutes (Schuster et al 1986). The plasma concentrations were some 10 times higher in the Jäger et al study, which could have been due to several factors, such as area
of skin used, inhalation of essential oil, vehicle used (Pinimenthol is an ointment) and the initial concentration in the administered product of the components measured. The Jäger et al study, while it did not control for inhalation, does closely approximate to what actually happens in aromatherapy massage. In fact typically the essential and fatty oil mix is applied to a larger area of skin, so it is possible
that higher plasma concentrations than those found for linalool and linalyl acetate will sometimes occur. In another study, dermal absorption of d-limonene via the hand was found to be low compared to inhalation exposure (Falk et al., 1991).
So from the data available, it seems the original texts and books on aromatherapy are right and thank goodness, because otherwise everything we have based our profession on would be useless. But it is fair to say that more controlled research needs to be done and to ensure inhalation is prevented to actually prove beyond doubt that dermal absorption does occur. I do believe that inhalation of the oils and the effect on the brain is as important in the use of aromatherapy as topical application but will leave this topic for another article!
In reality though, you cannot separate out the parts of an aromatherapy treatment as being more or
less important to the overall healing effect, although I appreciate that we need to have realistic evidence rather than just anecdotal reports. However, I have been working in this field since the early 1990’s and know from my own experience the amazing benefits aromatherapy brings to everyone who has presented themselves to me for treatments and I am sure ll aromatherapists will agree. Moreover, the real art of aromatherapy lies in its entirety. We could in fact say that an aromatherapy treatment is a synergy itself; the same word we use to describe a blend of oils “that the whole is greater than the sum of its parts”. The oils chosen for that individual is one element, then the carrier oil chosen for the skin is another element; we ensure that the client likes the aroma, which allows them to delight and relax within the fragrance, which itself is acting on the brain and the emotions through the limbic system; the oils’ molecules enter the bloodstream, then you have the relaxing environment created which the mind associates with pleasure and relaxation and finally the interaction between the therapist and the client and the caring, loving touch of the therapist’s hands, all adds up to the complete wonder that is aromatherapy.
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