Module 4: Skin Physiology - Summary

SUMMARY:

The principles of skin care:

The skin has developed to function effectively as a living structure at a liquid-air interface. The success of this interface is due to a specifically formulated combination of fatty substances that are bound between specifically adapted cells of the horny outer layer of the skin. A thin layer of oil rich secretions, secreted by the glands helps to maintain this barrier by acting as an endogenous emollient. The skin may be damaged in different ways and often there are multiple causes that contribute to a skin disease.

Absorption through the skin can occur in a normal skin with an intact barrier function. Substances that dissolve in organic solvents and are water insoluble (hydrophobic compounds) easily penetrate the fatty layer of the skin barrier. Although the mechanism is not well understood, water-soluble substances (hydrophilic compounds) can also penetrate the normal barrier, but at a much slower rate.

Areas not protected by the horny outer layers, such as the hair follicles sweat ducts and mucosal surfaces offer less resistance to the penetration of most substances, especially water-soluble compounds.

Damage to the skin barrier occurs easily. The fatty layer can be removed or damaged by detergents, organic solvents, soaps and chemicals. Too much water damages the specially adapted corneocytes by excess hydration (macerated skin), while an environment that is too dry, dries them out and disrupts the barrier. Once the barrier has been damaged, substances from outside can more easily penetrate the skin. This could result in stimulation of the skin inflammatory process or immune system and cause irritant or allergic skin diseases, such as contract dermatitis and urticaria. Systemic absorption is markedly increased through a damaged skin and can result in systemic toxicity. Infective organisms also gain easy access to the body via damaged skin.

Most people do not recognise that damage to the skin barrier occurs many times a day. Fortunately the skin barrier can regenerate, but requires time. We become aware of this damage when the skin shows changes such as, dryness, cracking and peeling. This represents early disease of the skin and is known as irritant dermatitis. Should damage occur faster than repair, a continuous state of disease will be evident as worsening dermatitis. Associated immune diseases, such as allergic contact dermatitis and urticaria and infections, occur more readily with damaged barrier function and thus often complicated the presentation of irritant dermatitis.

The skin is the largest organ in the body. It has adapted over millennia to operate as a living interface between the environment and the water rich milieu of the body. It is a highly complex organ essential to homeostasis. It is not to be seen in isolation. It incorporates and has in common many of the functional elements of the other systems such as the renal, cardiovascular, hepatic, gastrointestinal and neurologic systems. Dysfunction in any one of these systems could present as a skin manifestation.