Skin Deep: Dermal Absorption of Essential Oils

For one reason or another, many of us have applied essential oils topically, either neat (undiluted) or as a blend in a carrier, possibly as part of a clinical aromatherapy application. The integumentary system (the skin) is designed as a selectively permeable barrier to protect the human organism from its external environment.1,2 The inherent nature of the skin raises some curious questions with regards to essential oil applications, including: “How do essential oils pass through the skin?” “How readily do they absorb?” “Do essential oil constituents reach the blood stream? If so, how much? Enough to elicit systemic therapeutic effects?” and “Is there a way to increase penetration through and absorption into the various layers of the skin?” Scientific literature is offering great insight into these clinical aromatherapy questions.    

Basic Anatomy 101: The Integument

First, we must revisit basic anatomy and the layers of the skin. The outermost layer of the skin is the epidermis and it is comprised of 4-5 layers (depending on the location in the body). You may remember the mnemonic “Come, Let’s Get Sun Burned” or a similar tool to recall the layers from most superficial to deep: stratum Corneum, stratum Lucidum (palms and soles only), stratum Granulosum, stratum Spinosum, and stratum Basale. As cells mature, they progress from the stratum basale out toward the stratum corneum.2 By the time they reach the stratum corneum, they have become anucleated and highly keratinized. The highly keratinized nature of the stratum corneum renders it a highly effective protective barrier, especially from transepidermal water loss.1
The innermost layer of the skin is called the dermis. It consists of connective tissue, nerve endings, blood vessels, lymphatic vessels, sweat glands, sebaceous glands, and hair follicles. For the purposes of transdermal absorption, the dermis provides minimal interference. The most significant barrier of transdermal absorption is the epidermis.3 By the time the transdermal agent has passed through the epidermis and reached the dermis, it has now gained easy access to blood vessels for systemic circulation.2

Routes of Transdermal Absorption

There are three mechanisms for transdermal delivery: the intracellular route, the intercellular route, and the shunt route. The intracellular route is where molecules pass directly into the corneocyte (cells of the stratum corneum) and continue inward passing into and out of corneocytes along the way. Whereas, in the intercellular route, molecules are penetrating into the layers of the skin through the tiny spaces in between cells. The shunt route is a clever by-pass system where molecules do not directly pass through the corneocytes or the spaces in between them; instead, they pass through structures that originate in the dermis and span the entire height of the epidermis. Such structures include sweat glands, sebaceous glands, and hair follicles. By disrupting the keratin-rich epidermal layers, these structures allow for a significantly greater relative dermal absorption of molecules. As such, areas on the body that are plentiful in sweat glands, sebaceous glands, and hair follicles (ie. scalp, face) are great locations for absorption.4,5
Depending on the chemical nature of the transdermal agent (i.e. its molecular size, polarity), the path(s) that the agent uses and its degree of penetration are determined.  

Essential Oils: The Lipid-Lovers

As their name would imply, essential oil constituents are lipophilic (fat-‘loving’ or fat-soluble). This suggests that essential oils mix well with oils and poorly with water. As discussed previously, the keratinized nature of the epidermis is primarily designed to prevent desiccation; thus, the skin is a relatively lipophilic/hydrophobic barrier. Since both essential oils and the epidermis are relatively lipophilic, they ‘mix’ relatively well together, and therefore, essential oils have a greater tendency for transdermal absorption.

 

Factors Influencing Transdermal Absorption of Essential Oils

Many factors affect transdermal absorption rate and amount. Among them, surface area of the application, location of the skin application, exposure time, use of an occlusion technique, and temperature.1,2,4,5,6
As a general rule:

Factor Effect on Absorption
↑ Surface Area of Application ↑ Absorption
↑ Exposure Time ↑ Absorption
↑ Occlusion ↑ Absorption
↑ Temperature ↑ Absorption

Regarding location of the skin application, areas with the thinnest epidermal layers and areas rich in sebaceous glands, sweat glands, and hair follicles prove to be the best areas of transdermal absorption. These locations include face, neck, scalp, and wrist.4,5

From Skin to Blood

Research suggests that essential oil constituents are found in traceable amounts in the blood stream following topical applications. One study conducted with lavender essential oil tested for linalool and linalyl acetate (the two major constituents of lavender essential oil) in the blood following a gentle abdominal massage with a 2% lavender:98% peanut oil blend. Amounts of both constituents were identified 15 minutes after the beginning of the massage, with the peak occurring around 30 minutes. The study also calculated their half-lives: 13.76 minutes for linalool and 14.30 minutes for linalyl acetate. This demonstrates that these essential oil constituents do not remain in the blood stream for long and are readily metabolized by the body.7

Conclusion

Their lipophilic nature and small molecular size makes essential oil constituents great candidates for dermal absorption. In fact, these fragrant molecules are able to enter the bloodstream through such topical applications in quantifiable ways.7 Many factors influence transdermal absorption; by understanding the science of essential oils and the physiology of the body, we can target our therapies and maximize our aroma-therapeutic effects.

References

  1. Menon GK, Cleary GW, Lane ME. The structure and function of the stratum corneum. International Journal of Pharmaceutics. 2012;435:3–9.
  2. Graham-Brown R, Burns T. Dermatology (9th ed.). Oxford: Blackwell, 2007.
  3. Andrews SN, Jeong E, and Prausnitz MR. Transdermal delivery of molecules is limited by full epidermis, not just stratum corneum. Pharm Res. 2013;30(4):1099–1109.
  4. Mohammed D, Matts P, Hadgraft J, Lane M. Variation of stratum corneum biophysical and molecular properties with anatomic site. AAPS Journal. 2012;14(4):806-812.
  5. Rougier A, Lotte C, Corcuff P, Maibach H. Relationship between skin permeability and corneocyte size according to anatomic site, age and sex in man. J Soc Cosmet Chem. 1988;39:15–26.
  6. Berthaud F, Narancic S, Boncheva M. In vitro skin penetration of fragrances: Trapping the evaporated material can enhance the dermal absorption of volatile chemicals. Toxicology in Vitro. 2011;25:1399–1405.
  7. Jager W, Buchbauer G, Jirovetz L, Fritzer M. Percutaneous absorption of lavender oil from a massage oil. J Soc Cosmet Chem. 1992;43:49-54.

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Timothy Miller ND, LAc, RA

Timothy Miller ND, LAc, RA is a naturopathic physician, licensed acupuncturist, and registered aromatherapist. He is a graduate of the National College of Natural Medicine (NCNM) in Portland, OR.

Dr. Tim is a chemistry nerd. He is fascinated by the chemistry found in the natural world. Fueled by the abundant, potent, and unique components within aromatherapy, Dr. Tim has sought to understand how essential oils act on the body and identify which clinical applications are best incorporated into practice.

Dr. Tim first began his aromatherapy studies in 2005. He has since traveled the world to advance his understanding of essential oils and their clinical implications. Dr. Tim has studied with Rhiannon Lewis, Mark Webb, Gabriel Mojay, Kurt Schnaubelt, and Jeffrey Yuen. He has successfully completed a National Association of Holistic Aromatherapy (NAHA) approved course and has completed the requirements to become a registered aromatherapist. He is a member of the Aromatherapy Registration Council (ARC).

Beyond his love of aromatherapy, Dr. Tim is an avid traveler and student of foreign languages. He enjoys spending time with his family, watching movies, and being in nature. Dr. Tim loves to learn new things and is driven by self-improvement and emotional intelligence.

Dr. Tim believes deeply in Docere and loves to teach. He is an international speaker, workshop leader and contributing author. He believes learning should be fun and makes every attempt to engage his students in a profound and meaningful way.

Dr. Tim has taken part in several podcasts discussing a range of topics. Please find them below:

1. AromaChemistry with Dr. Tim – NAHA’s Beyond Aromatics Podcast
2. How to Fall in Love with Essential Oil Chemistry with Dr. Tim – Atlantic Institute of Aromatherapy and Nyssa Hanger
3. Conscious Living with Dr. Tim – The Orson Wells Show
4. The Naturopathic Journey with Dr. Tim – Eight Billion Podcast
5. Don’t Throw Away Your Shot with Dr. Tim – LabAroma Podcast