Dermatology is the branch of medicine that deals with conditions of the skin.The skin is also valuable for diagnosis of other conditions, since many medical signs show through the skin. Skin color affects the visibility of these signs, a source of misdiagnosis in unaware medical personnel. Society and culture
Hygiene and skin care
The skin supports its own ecosystems of microorganisms, including yeasts and bacteria, which cannot be removed by any amount of cleaning. Estimates place the number of individual bacteria on the surface of 6.5 square centimetres (1 sq in) of human skin at 50 million, though this figure varies greatly over the average 1.9 square metres (20 sq ft) of human skin. Oily surfaces, such as the face, may contain over 78 million bacteria per square centimetre (500 million per square inch). Despite these vast quantities, all of the bacteria found on the skins surface would fit into a volume the size of a pea. In general, the microorganisms keep one another in check and are part of a healthy skin. When the balance is disturbed, there may be an overgrowth and infection, such as when antibiotics kill microbes, resulting in an overgrowth of yeast. The skin is continuous with the inner epithelial lining of the body at the orifices, each of which supports its own complement of microbes. Cosmetics should be used carefully on the skin because these may cause allergic reactions. Each season requires suitable clothing in order to facilitate the evaporation of the sweat.
The main cell types are fibroblasts, macrophages and adipocytes (subcutaneous tissue contains 50% of body fat). Fat serves as padding and insulation for the body. Cross-section
Development
Skin colour
Human skin shows high skin colour variety from the darkest brown to the lightest pinkish-white hues. Human skin shows higher variation in colour than any other single mammalian species and is the result of natural selection. Skin pigmentation in humans evolved to primarily regulate the amount of ultraviolet radiation (UVR) penetrating the skin, controlling its biochemical effects.The actual skin colour of different humans is affected by many substances, although the single most important substance determining human skin colour is the pigment melanin. Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin colour of darker-skinned humans. The skin colour of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the haemoglobin circulating in the veins of the dermis. The red colour underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or the stimulation of the nervous system (anger, fear), arterioles dilate.There are at least five different pigments that determine the colour of the skin. These pigments are present at different levels and places. Melanin: It is brown in colour and present in the basal layer of the epidermis. Melanoid: It resembles melanin but is present diffusely throughout the epidermis. Carotene: This pigment is yellow to orange in colour.