Functions of the skin

The skin acts as a protective covering to the body. Its functions are as follows:
• It forms a physical barrier to antigens or bacteria.
• It prevents excessive absorption or loss of water.
• Its pigmentation prevents injury from ultraviolet (uv) light.
• Vitamin D is synthesized by sunlight in the epidermis.
• It is involved in temperature regulation.
• Sensations of pain, touch and temperature can be distinguished.
• It is involved in immunological reactions


The history should include questions on the patient’s general health, past medical history, family history, occupation and any drugs being taken. A description of the skin lesion should be obtained, including its site of origin, spread, length of time it has been present, whether it is itchy (Information box 20.2) or painful, whether it forms blisters or whether any ointment or medicines have helped.


A careful examination of the whole skin should be made, as clues to the diagnosis may be apparent in distant sites. If the nature of the skin disease is not obvious, a full general examination should be performed, as the skin disease may be a manifestation of a systemic disorder.

Pruritis means itching. It can occur in many skin conditions, including:
Atopic eczema

Insect bites (e.g. flea, bed-bug)

It also occurs with systemic conditions, often without obvious skin involvement. These include: Metabolic disease-hyperthyroidism, carcinoid syndrome Malignant disease-chronic lymphatic leukaemia, lymphoma, some carcinomas Haematological disease-polycythaemia vera Renal disease-chronic renal failure with uraemia Liver disease-cholestasis, particularly primary biliary cirrhosis
Miscellaneous-senile pruritus, psychogenic, drugs, e.g. opiates

WOOD’S LIGHT. This is a UV light that is shone on the skin. ormal hair and skin fluoresce bluish-white. Certain types of ringworm (Microsporum audouini and M. canis) fluoresce a greenish colour; erythrasma due to Corynebacterium minutissimum fluoresces pink/red. PATCH TESTS. (Practical box 20.1). These are used to confirm allergic contact dermatitis. LABORATORY TESTS for the exclusion of bacterial and fungal infections. Tests for SLE or thrombocytopenic purpura, for example, should be performed as appropriate. HAIR-microscopy and root analysis.
ROUTINE TESTS such as blood counts and erythrocyte sedimentation rate (ESR) and also urine testing, e.g. for glucose in diabetes, should be performed.

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