Did you know that the skin is the most voluminous organ in the human body, comprising as much as 15% of the total adult body weight?

In this two part overview we will explore a a few facts about this incredible organ and how aromatic therapy can help support and maintain healthy skin

Part 1 is a brief overview of the structure and basic functions of the skin and how compounds such as essential oils are absorbed.

Part 2 will discuss the issues of skin integrity and the ways in which essential oils can help support the its capacity to defend itself and heal

What is the skin?

Skin is the main barrier between the internal body and the external world, protecting the body against biological, chemical, mechanical, and ultraviolet threats and contaminations.

Deeply sensitive and resilient, the skin is a super-organ, maintaining systemic homeostasis responsible for:

• thermoregulation

• preventing excess water loss

• absorption and elimination

• vitamin D synthesis

• mediating the interrelationships between the immune, neurologic, and endocrine systems. 

Human skin is made up of three layers

the epidermis

The epidermis is the outermost layer, the skin barrier, and protects the body from potentially damaging environmental factors. The epidermis, is characterised by a constellation of tough cells known as keratinocytes. These cells synthesizse the protective protein keratin, a fibrous alpha-helical filament that renders the epidermis strong and flexible, and waterproofs the surface of the skin. 

the dermis

It is the thickest layer, made of dense connective tissue with blood and lymph vessels, nerves, hair follicles, and glands. The thick layer of dense connective tissue is primarily composed threadlike fibers1 of structural protein collagen.

 Collagen production in the dermis gives the skin its strength and flexibility, 

the hypodermis

Also called the subcutaneous tissue layer. It’s is mostly made up of fatty and connective tissues that house larger blood vessels and nerves and helps insulate the body from heat and cold. The hypodermis thus regulates body temperature. 

Skin is the body’s barrier

As mentioned above, the epidermis acts as a barrier against external contaminants.

The skin barrier has a critical function in maintaining skin integrity through :

• skin permeability

• prevention of water loss

• antimicrobial protection

• protection against UV radiation damage. 

Elements of the skin barrier are

• the stratum corneum, made up of cells called corneocytes that act as bricks.

• The lipid matrix is a mortar-like substance, comprised of fats such as ceramides, cholesterol, and fatty acids. This layer also contains a protein called filaggrin, which helps make natural moisturising factors for the skin.

• The tight junctions connect neighbouring cells tightly together and help prevent the penetration of unwanted substances between those cells.

The integrity of these elements will affect the permeability of the skin and the absorption of EO constituents.

Penetration and absorption

Essential oils are made up of tiny chemical constituents which can easily penetrate to be absorbed by the skin. When applied on the skin, EO constituents pass from the stratum corneum into the lower layers of the epidermis to be absorbed into the lymphatic system via the tissue fluids and from there will eventually reach the bloodstream

Essential oils constituents have different densities and generally tend towards being lipophilic (fat-loving) although some are more hydrophilic (water-loving). It is these oil or water friendly qualities that will determines how easily or quickly they will penetrate the skin barrier and by which path or route they will tend to make their way through the stratum corneum.

Three routes of absorption:

1. Intracellular penetration through the corneocytes, More water friendly constituents will prefer to traverse the epidermis via the intracellular route

2. Passage through intercellular spaces. More fat-friendly constituents will tend to cross the stratum corneum via the intercellular passage

3. The transappendageal route, via the sweat glands and along hair follicles with their associated sebaceous glands This route bypasses penetration into the stratum corneum. . 

Absorption in aromatic practice

The aromatic therapist’s decision on the best manner of application of an essential oil treatment will depend on the purpose and action required by the client.

For instance, in general skincare treatments, absorption into the bloodstream is neither necessary nor desirable as we want to keep EO constituents actions to benefit the epidermis/dermis layers as long as possible. 

In the case of treatments for joint or muscle pain and inflammation, some absorption of essential oil constituents into the systemic bloodstream is required.  Although treatments for joint or muscle tissues aim at being locally effective, it may be useful for constituents with pain relieving properties to enter into the bloodstream to eventually reach the brain for their analgesic and antinociceptive actions.

Factors to be considered

1.Method of Application

Applying EOs to the part of the body with the thinnest skin such as the inner wrists and ankles, behind the knees and inside the elbow, on the neck and temples will increase transdermal absorption to some degree 

Application to a larger area of skin, as in a full body massage can result in the highest absorption. Additionally, the mechanical friction from massage improves the absorption  by increasing blood flow and temperature, as well as changing the structure of the stratum corneum, making skin even more permeable. 

2. Environmental factors

Such as UV exposure, air pollution and tobacco smoke, iadded to genetic factors can impair the barrier function of skin, which in turn leads to increased loss of water, and structural changes in the stratum corneum. The consequence is increased skin permeability, which makes already damaged skin even more exposed  and vulnerable to irritants. 

3. Dose and dilution

Safe and appropriate dose and dilution, usually in vegetable oils, also influences the absorption rate.  Although undiluted EOs could result in a higher concentration of constituents in the skin compared to diluted EOs, the increased risk of adverse effects such as irritation and allergies, makes such use highly undesirable. Additionally, research has shown that higher concentration to actually show lower absorption.  However there are Eos, such as lemon, that are known to act as skin penetration enhancers. I will talk more about the use and mechanism of penetration enhancers in Part 2.

4. The base

The base, or vehicle, in which EOs are diluted will also influence the rate of absorption. Vegetable oils are the most common bases for dermal conditions and skincare but there are studies comparing the absorption rate of EO constituents in a hydrogel (water-based gel), emulsion or oil show that constituents from the hydrogel base penetrated the skin most efficiently. 

The greater absorption from a hydrogel can be explained by the tiny lipophilic (oil loving) EO constituents will naturally seek to migrate into the more lipophilic medium of the stratum corneum. 

However, depending on the purpose of the treatment this does not mean that a gel is always the most appropriate vehicle. For example Tamanu oil has anti-inflammatory and nervine actions which are particularly helpful for sciatica.

As already mentioned, a vegetable oil base will be more appropriate to treat skin care and healing where you want the essential oils to act on the surface, whereas, a hydrogel will be appropriate for muscular and joint pain wound healing, where you want the Eos to penetrate into the tissues. 

Disturbed skin barrier function

Disturbed barrier function may allow potential toxins and allergens to penetrate the skin more easily. The causes may be due to

• ageing

• UV rays

• sleep

• allergies

• hormonal changes

• genetic influences

• excessive smoking

• alcohol consumption

• unhealthy life-style habits and nutrition

• psychological stress

• seasonal or climate changes

Disturbed barrier function is often associated with excessively dry skin and is at the origin of various skin conditions such as eczema and psoriasis.

To summarise

We learnt a little about this amazing organ and how it functions.

All too often, though, we take our skin for granted and overlook the need to look after and nurture this precious physical boundary so that it continues to offer us optimal protection from the adverse elements of our environment and lifestyle choices.

Caring for our skin is as important to our wellbeing as fixing a leaky roof over our heads. Neglect of our skin allows toxins to seep into our bodies, causing disarray to our physical and emotional wellbeing.

Part 2 of this article will explore further the different consequences of disturbed skin barrier and suggest how to foster better care through including essential oil products in our skincare rituals.

References

Bensouilah, Janetta,Buck, Philippa. Aromadermatology: Aromatherapy in the Treatment and Care of Common Skin Conditions (p. 206). CRC Press

Jade Shutes, study notes from my ongoing studies at School of Aromatic Studies

Cal, K. (2006). Skin penetration of terpenes from essential oils and topical vehicles. Planta Medica, 72, 311–316. http://doi.org/10.1055/s-2005-916230

Harding, C. R. (2004). The stratum corneum: structure and function in health and disease. Dermatologic Therapy, 17, 6–15. https://www.ncbi.nlm.nih.gov/pubmed/14728694

Mojumdar, E. H., Gooris, G. S., Groen, D. et al (2016). Stratum corneum lipid matrix: Location of acyl ceramide and cholesterol in the unit cell of the long periodicity phase. Biochimica et Biophysica Acta, 1858, 1926–1934. http://doi.org/10.1016/j.bbamem.2016.05.006

Tagami, H. (2008). Location-related differences in structure and function of the stratum corneum with special emphasis on those of the facial skin. International Journal of Cosmetic Science, 30, 413–434. http://doi.org/10.1111/j.1468-2494.2008.00459.x

Tisserand, R. Young, R. (2014). Essential oil safety, 2nd edition. Churchill Livingstone, Edinburgh http://roberttisserand.com/essential-oil-safety-book-second-edition/

Wertz, P. W. (2018). Lipids and the permeability and antimicrobial barriers of the Skin. Journal of Lipids, 2018. http://doi.org/10.1155/2018/5954034