What is skin?

The basic definition of skin both in a medical and English dictionary describes it as the external layer of the body. But this description is really wholly inadequate. It infers that the skin is an inert envelope that contains the bones, muscles, organs and blood that allow us to exist. Whilst the skin is our external covering that holds us together, it is far from inert. To express it creatively, the skin is a combination of a lunar landscape, a zoological and botanical haven in which there is the potential for an immunological party. Expressed more traditionally, the surface of the skin is a rough, undulating environment with skin cells desquamating all the time. It is covered with bacteria and fungus that live in harmony with us and protect us from invading pathogens. In a normal state the immune system within the skin is quiet and relatively inactive, but if the skin is challenged in any way, a range of immunological cascades are set in motion. In some conditions such as psoriasis these immunological changes are not within a normal range and cause severe inflammation and hyperproliferation of skin cells.

Defining the skin as our external surface is also limited because it does not include our internal skin surfaces such as the mouth or the vagina. And of course the scope of the term dermatology goes beyond what is traditionally described as skin to an interest in both hair and nails, commonly thought of as skin appendages which are constructed of the same basic building blocks as skin itself.

Understanding of the science of skin is constantly expanding. Of key importance in improving understanding of skin and how it functions, is research. Important areas of biological scientific research include how the immune system within the skin functions and how genetic makeup influences the expression of skin disease and how humans respond to treatment. But to truly understand ‘What is skin’ we must gain insights that go beyond comprehending physical function. Research can also help to uncover some of the psychological and social impacts of experiencing skin disease. For example what affects how people cope with a chronic condition and how quality of life might be affected?
What is skin for the lay person? The way the skin looks plays an important role and the aesthetics of the skin are considered shortly, but the skin has also influenced our language in all sorts of colourful ways. Skin can probably win the prize for the organ most used in common parlance and slang! Table 1.1 gives some examples. This reflects the cultural and symbolic importance of skin as an integral part of our language.

Table 1.1 The use of the skin concept in common parlance.   Saying Meaning   By the skin of one’s teeth By a narrow margin   Get under someone’s skin To irritate or provoke someone   No skin off someone’s nose No disadvantage to someone   Skin and bone Very thin   Skin-up Roll a joint   Skin deep Superficial   Skin-flick A film of adult nature involving nudity   Skinful A large amount to drink   Skin game A swindling game or trick   Skin and blister Sister (Cockney rhyming slang)   Have a thick skin To be unbothered by things   Save ones skin To avoid harm especially escaping death