The Transdermal Absorption of Essential Oils: The what, where and how they influence our bodies!
A Study on the Absorption of Essential Oils
Written by Tillie Alenikoff
Essential oils have been used for thousands of years by many cultures for various reasons, even before they could be fully understood. In today’s world, we use essential oils for many things and they are utilized by people of all sorts, ranging from medical doctors to the average Joe. You will see people diffusing them, using them topically, and even taking them internally. Interestingly, the last couple of decades has allowed science to verify what our history books have already implied. Essential oils are one of man’s first prescriptions! With research comes discovery and influence over our use of essential oils; such as where to apply them to create the best effects, and which ones to apply for a specific concerns or aliment. One of the most common ways essential oils can be used is topical application aside from inhalation; for the purpose of this paper our focus will remain here.
At some point, many of us have used essential oils undiluted or diluted for something; in a perfume, a massage oil, lotion, soap…the list is endless. The skin is designed to protect but also selectively allow things from our world/ environment in. This can raise questions though- How are they absorbed? Where do they go once absorbed? Should they be used on specific part of the body? Can absorption be increased? As we know, the skin forms a barrier of protection between us and our environment. It holds all our internal organs together, keeps many toxins and chemicals out and acts as a first defense for our bodies.
Before discussing how essential oils get into the body, take a moment to understand what they are trying to pass through. The epidermis is the outermost layer. This layer acts as a barrier that an essential oil would need to break through to get to the dermis. This part of the skin is made up of a few different layers that change as the skin matures or ages, going through a process called ecdysis. (4) This process is continual, the speed of this process can be affected by age (we tend to have less collagen leaving us with thinner skin and slower cellular turnover), health (some immune compromising conditions can reduce the speed at which this process occurs and efficiency), and environment (the keratinized structure of the skin can be thicker, also consider living in a cooler or hotter climate affecting the viscosity of the essential oil or our own sebum). The number of layers in the epidermis can depend on the part of the body, ranging between 4 or 5 layers from most superficial to deep: stratum corneum, stratum lucidum (palms and soles of the hands and feet), stratum granulosum, stratum spinosum, and stratum basale. As cells proceed to go through the action of ecdysis, they progress from the stratum basale, out toward the stratum corneum, by the time they reach the stratum corneum, they have formed a layer of dead cells that are highly keratinized. The highly keratinized nature of the stratum corneum renders it as a highly effective protective barrier for our bodies. (1)
The innermost layer of the skin is called the dermis. It consists of connective tissue, sweat glands, nerve endings, blood vessels, sebaceous glands, lymphatic vessels, and hair follicles. For the purposes of absorption of essential oils, the dermis is generally where all the action happens. By the time an essential oil has passed through the epidermis and reached the dermis, it has now gained easy access to blood vessels. This means that the essential oil has access to the entire body gained through our circulatory system. (1)
There are three forms of transdermal absorption, this process not only applies to essential oils but our cosmetics and skin care products. First the intracellular route (inside the cell), the intercellular route (outside the cell), and the shunt route (a direct bypass). The intracellular route is utilized when molecules pass directly into the cells of the stratum corneum, and continue inward, passing into and out of cells along the way. With the intercellular route, molecules are penetrating into the layers of the skin through the tiny spaces in between the cells. The shunt route is a bypass system in which molecules do not directly pass through the cells or the spaces in between them; instead, they pass through structures in the dermis and go through the entire epidermis. These include sweat glands, sebaceous glands, and hair follicles. (2) Because these structures continue through the epidermal layers they provide an easy bypass for essential oils to pass into the body and then blood to circulate through the body. So, this would imply that areas that tend to have more sweat glands, sebaceous glands, and hair follicles are great locations for absorption (the scalp or face) of essential oils.
I must digress for a moment! How small do these molecules need to be to even pass through epidermis and dermis? How small do they need to be to pass into the blood stream? Can they pass into the tissue of the brain? Most topical supplements, cosmetics, and prescriptions follow the 500 Dalton Rule, this is a rule of measurement for the weight of a molecule. If the molecule is above 500 Daltons, molecularly it is too large to pass through the skin. This is a rule most used for cosmetic and aesthetic products. (3) So, one Dalton is equal to one AMU (Atomic Mass Unit). When looking at gas chromatography and mass spectrometry (GC/MS) analysis of an essential oils, you will notice a breakdown of terpenes (monoterpenes, sesquiterpenes, and diterpenes), and the oxygenated compounds which are mainly esters, aldehydes, ketones, alcohols, phenols, and oxides, these can all be measured in AMU’s. Most essential oils will fall under 500 AMU, but there are other factors that influence their absorption- they must be fat soluble. (5)
Essential oil constituents are fat-soluble. By definition, this means a substance that can dissolve in fats and oils. Many vitamins in our supplements and foods are considered fat-soluble such as vitamins A, D, E, and K. This would imply essential oils would mix well with other oils. Our sweat glands, sebaceous glands, and hair follicles excrete sebum, this provides a mixture of triglycerides, wax esters and metabolites; this may be another factor as to why the shunt route provide a perfect direct access to rest of our body, acting as a carrier for essential oils.
Absorption of Essential Oils
Many things can influence absorption of essential oils; we will discuss just a few key factors: temperature, location of application, and use of carrier oils. Temperature can affect the viscosity of oils; a higher temperature means more viscosity or movement. Waxes and triglycerides in the skin may not have the same viscosity in 30-degree weather as it would in 80-degree weather. The same would apply to the essential oil and carrier oil used. This can slow the rate of absorption. We have already touched on location- areas of the body that are denser in sebaceous glands (face), sweat glands (neck/ chest), and hair follicles (scalp), prove to be the best areas of absorption. Carrier oils may sound simple enough, but there are many different types of carrier oils. The viscosity and presence of certain constituents in these can influence choosing a carrier oil for your essential oil blends depending on what and where your intention for use is. For example, Jojoba oil would be better used as a carrier oil for a facial blend as the components mimic our own sebum and collagen; allowing this carrier oil to sit well on the skin. (7) Another example: you have created a beautiful essential oil blend but you would like it to linger once applied topically, in this case you may want to pick a heavier or thicker carrier oil such as olive oil or even a butter like shea or cocoa, as it will prevent quick evaporation of your essential oil once applied.
So, we now have a better idea of how these essential oils get into our bodies and ways to increase their absorption. But want happens after that? You can google essential oils in the body- Doing this, hundreds of articles, studies, and posts popped up. Finding a ton of general information regarding this subject, but actual studies? Numbers? Taking a step back knowing essential oils molecularly must be a certain weight to gain access topically. Remember essential oils have constituents that make up their AMU’s and all the positive properties we are trying to look at. So, let’s take a quick look at terpenes one of the most common constituents in essential oils. Terpenes are made up of monoterpenes, sesquiterpenes, and diterpenes. So, we don’t have to go through an entire chemistry lesson but to provide some ground to discuss let’s just stick with monoterpenes at this point. There are different types of monoterpenes found in essential oils such as Camphene, Carene, Cymene, Limonene, linalool, Myrcene, Pinene, Terpinen and α-Terpineol to name a few. Each of these chemical components have their own therapeutic properties such as antiseptic, analgesic, rubifacient, decongestant, antibacterial, and some even act as skin enhancers. (8)
Understanding that these chemical components are what we are really looking at regarding positive measurable therapeutic effects can insert the knowledge needed to utilize these oils on a much deeper level. Each of these constituents can be found at varying levels in different essential oils. This allows us to pick and choose which essential oil would benefit us for a specific ailment after identifying which components provide the medicinal benefit we are trying to achieve.
Lavender oil has been produced and used or a large scale in many countries for health and beauty products. One form Lavandula angustifolia has been used for hundreds of years for various conditions such as insomnia, alopecia (hair loss), anxiety, stress, and postoperative pain. One study focused on Lavender oil constituents in the blood after topical application. measuring the two-main constituent’s linalool 1 and linalyl acetate found in the essential oil. In this study Lavender massage oil diluted with peanut oil was massaged over the abdominal area of a male subject, what did not absorb wash wiped away. Blood samples were obtained at intervals from the initial application up to 90 minutes. The blood specimens had heparin added to them and were centrifuged to separate the plasma. The plasma was then used for measuring the constituent’s linalool and linalyl acetate in a gas chromatography. These could be measured in the blood just five minutes after application with a peak after 20 minutes of application, noting the dissipation of the constituents to almost zero at 90 minutes. (9) Another study used the Lavender as a massage oil but for discomfort and pain associated with dysmenorrhea. Through this study a significant reduction in associated pain was noted as well. The author made indication that linalool and linalyl acetate in the essential oil absorbed through the skin could have an affect over the central nervous, allowing relaxation in turn alleviating stress and anxiety. (10) This effect can also correlate to the countless remedying suggestions to use lavender for sleep.
The properties that essential oils hold and the effects on our bodies can be incredible. When properly distilled at the right time, the combination of constituents can act as a powerful remedy for varying conditions. With the advancements in science, our society has the ability to not only recognize the chemicals in our essential oils but to also test and study the effect they have on a cellular level. Numerous studies are available on the antitumoral effects of many constituents- these studies look at the individual property vs a type of cancer cell; colon, breast, prostate… etc. and which one has a greater affect. A number of these studies look at the synergistic effect of the essential oil as well noting not only the antitumoral effects but the inhibition of pro-inflammatory markers. Some of these studies suggest antioxidant involvement as well noting a certain constituents’ roles in suppressing the cell signaling and pathway generation for additional inflammatory and cancer cells to form. These studies also suggest that the constituents also recognize the morphed cell and has the ability to leave good cells alone while causing cell death in others. (12) One study noted Tea Tree oil and its cytotoxic effects to remove transient flora while inhibiting the commensal flora but not causing cell death. (11)
Melaleuca alternifolia (Tea Tree) Oil is one essential oil that has been widely studied for its antimicrobial, antibacterial, antifungal and other properties. There are many types of Melaleuca, over 150 species but alterfolia contains just the right constituents in the essential oil once extracted to provide health benefits and additionally when used in therapeutic amounts can be considered non-irritating when used topically. Studies have confirmed that the presence of terpinen and α-terpineol in Melaleuca alterfolia contributes to the essential oils widely used antibacterial and antifungal properties. (13) These constituents can act as abrasives to the liposomes of the cell wall of an unfriendly fungal or bacterial cells. The combination of properties can even prevent unwanted cells from forming reproductive means, disrupting their morphology for a period. This could imply that when using Melaleuca alterfolia in conjunction with other modalities to treat a staph infection of the skin (which is the abnormal growth of Staphylococcus aureus now out numbering communal flora of the skin), one could inhibit the reproduction of the staph and then kill off the over production. Understanding that the use of specific constituents of an essential oil to penetrate the skin and proliferate a cell wall, producing positive outcomes when using therapeutic doses can be achieved. (14)
The premises that essential oils can be absorbed transdermal and utilized for their therapeutic effects was anything but an old wives tail. Chinese medicine, Greeks and Egyptians have used them for thousands of years without the use of a microscope or biological understanding. Before the science was available, essential oils were thought to hold a place between health and spiritual connection. This is a belief that is still held today in many cultures. Through trial and error, accidental use or even intuition essential oils and herbal concoctions were used to treat the body and the mind with great success. Many treatments used a hundred years ago are still applicable today.
Simply using Lavender before bed to help with sleep aromatically or topically can benefit a person in more ways than they may have initially intended. It may help with sleep causing relaxation and in turn reduce stress, lower cortisol levels, this in itself can lead to a positive attitude, focus, and better social interactions. Essential oils have hundreds of constituents that can have synergistic effect on the body as a whole. As humans, we are always looking for answers, time has shown that we are capable of understanding the body on levels not thought of by our predecessors. Furthermore, we are not at the climax. In fact, the 21st century has opened up new avenues for research and treatment which will lead to clinicians & aromatherapists globally having a greater understanding of how a substance can absorb into the body, while further understanding the molecular construction and cellular interaction that makes use of a natural world of healthcare that has been in front of us a very long time. Nature called in man’s prescription, we just need to pick it up!
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11. Hammer KA1, Carson CF, Riley TV.,” Susceptibility of transient and commensal skin flora to the essential oil of Melaleuca alternifolia (tea tree oil).”, 1996 Jun;24(3):186-9.
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