More information about the skin

The Skin

The basic structure of skin is a thin outer layer called the epidermis overlying a thick inner layer called the dermis, under which there is a layer of fat. Within the dermis there are blood vessels, sweat glands, nerve endings that are sensitive to pain, pressure, touch and itch and, in hair bearing skin, hair follicles and their associated glands and small muscles (which make the hairs stand up in response to cold, producing goose-pimples, and sometimes also in response to fear, when our hair stands on end). Skin cells are formed continuously within the epidermis, migrating towards the surface where they lose their nuclei and become dead cells containing keratin - a process that takes about 30 days from start to finish. Also contained in the epidermis are cells called melanocytes which secrete the pigment melanin, which protects the skin from the effects of the ultraviolet light in sunlight, and cells of the immune system. The skin structure is adapted in different parts of the body to meet the demands made upon it - that's why it's thicker on the sole of the foot than the back of the hand.

The skin responds to many underlying disorders by producing changes, some of which may also be produced by disorders of skin itself. They may be localised to a particular area, as with, for example a cold sore on the lip caused by herpes simplex, or affect the whole body, as is the case with chicken pox, caused by infection with the virus herpes zoster. They may or may not be accompanied by other symptoms such as pain or itching.

Many conditions produce rashes, which are described by their colour and shape: if it's red it's called erythematous, and if it’s due to the dilatation of blood vessels in the skin it fades, or blanches, if you press on it with a glass. If it’s due to bleeding into the skin it’s called purpura, and it doesn’t blanch when you press it. If it's flat and less than half a centimetre in diameter it's called macular, if it’s raised it’s called papular. If the inflammation occurs under the skin producing lumps they’re called nodules, while if it occurs at the surface of the skin producing spots filled with fluid they're called vesicles if they’re less than half a centimetre, and bullae if they’re greater. If it's filled with pus it’s called a pustule. Superficial breaks in the skin surface, just affecting the epidermis, are called erosions, and they heal without scarring, while breaks that affect the underlying dermis are called ulcers and when they heal it usually occurs with scarring.