The skin is very much more than just an outer covering wrapping up the 'parcel' that is your body. It is the largest organ of the body and of the integumentary system made up of multiple layers of mesodermal tissue, and guards the underlying muscles, bones, ligaments and internal organs. Because it interfaces with the environment, skin plays a key role in protecting (the body) against pathogens and excessive water loss. Its other functions are insulation, temperature regulation, sensation, synthesis of vitamin D, and the protection of vitamin B folates.

It is also vitally important in aromatherapy, because it is one of the two routes by which essential oils can get into the bloodstream, and thus travel round the body (the other being via the lungs).

Skin has mesodermal cells, pigmentation, or melanin, provided by melanocytes, which absorb some of the potentially dangerous ultraviolet radiation (UV) in sunlight. It also contains DNA-repair enzymes that help reverse UV damage, and people who lack the genes for these enzymes suffer high rates of skin cancer. One form predominantly produced by UV light, malignant melanoma, is particularly invasive, causing it to spread quickly, and can often be deadly. Human skin pigmentation varies among populations in a striking manner. This has led to the classification of people(s) on the basis of skin color.

As mentioned above, the skin is the largest organ in the human body. For the average adult human, the skin has a surface area of between 1.5- and 2.0 square meters (16.1-21.5 sq ft.), most of it is between 2-3 mm (0.10 inch) thick. The average square inch (6.5 cm²) of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand nerve endings.

The skin is a giant organ of elimination, getting rid of the waste-products of many bodily processes through the pores, carried in sweat. If the other organs of elimination {the kidneys and colon) are not working as efficiently as they should, a variety of skin diseases, ranging from eczema to acne and boils, may occur because the body is trying to push out through the skin more toxins than the skin can effectively cope with.

If the skin allows certain substances to pass out of the body, while safely containing others, it is equally true that it can absorb some substances into the body while excluding many that could harm the muscles and organs beneath it. Because of this, the skin is described as 'semi-permeable'.

The factor which determines whether any particular substances will be able to pass through the skin or not, is the size of the molecules from which it is made up. Essential oils have a molecular structure which is relatively small and simple, and they pass through the skin easily. This has been clearly demonstrated in an experiment in which oil of garlic was rubbed into the skin of a volunteer's foot: ten minutes later the garlic was measurable on his exhaled breath. This means that in ten minutes, the garlic oil had passed through the skin and been absorbed into the bloodstream, and had already reached the deoxygenatcd blood being returned to the lungs.

Not all essential oils pass through the skin quite so quickly. It may take several hours for the oils used in a bath or massage to be completely absorbed into the body, but a part of the oil will usually reach the bloodstream quite soon after first being applied to the skin.

A second factor which enables essential oils to be absorbed by the skin is the fact that they dissolve easily in fatty substances. The skin produces its own protective layer of an oily wax, called sebum, and in this the essential oils can dissolve, making their absorption by the skin even easier.

Immediately below the skin, the particles of essential oil pass into the fluid that bathes every cell of the body, and from here they can pass through the ultra-thin walls of the lymph ducts and tiny blood-vessels (capillaries). In this way, the aromatic particles pass into the general circulation, and travel around the body.

This gives us a very effective, and very safe, method of getting essential oils into the body when needed. In a crisis, such as an infectious illness, more essential oil can be absorbed into the body by massaging the back at half-hour intervals, then couid be given by mouth in the same period of time without irritating the stomach lining.

A few sensible precautions are needed, such as diluting essential oils in a carrier, usually a 3% dilution, before massage, avoiding oils known to be irritant to the skin, and, in the case of people with sensitive skins, checking their reaction by trying an oil on a very small area first.

Essential oils can contribute enormously to the health and appearance of the skin itself, and this is discussed in the entries for DRY SKIN, OILY SKIN, IRRITATED SKIN, SENSITIVE SKIN, WRINKLES, SKIN PATCH TEST, and also ACNE, DERMATITIS, ECZEMA and PSORIASIS as well as entry under SKIN and SEBUM which gives a fuller account of the functions of the skin and how Essential Oils interact with it.