Two fundamentally different forms of pigmentation of the skin are distinguishable, according as the pigment arises by intracellular metabolism or is directly derived from the blood-pigment. The latter occurs in cases of haemorrhage or of prolonged hyperemia, as in the neighbourhood of varicose ulcers and in the cicatrices after the healing of these.

Of more importance is the true Melanotic pigmentation. This is illustrated in Addison's disease (see under Intoxications), where there is a bronzing of the skin chiefly in the exposed parts. The pigment here is in the deeper layers of the epidermis and more superficial layers of the cutis. Syphilis is also a cause of pigmentation. Most chronic syphilitic lesions of the skin are accompanied by and leave behind a coppery coloration.

Chloasma is a local pigmentation of the skin which has mostly a reflex origin. It occurs chiefly during pregnancy, brown coloration of the face developing pathologically as brown coloration of the nipple and areola develop physiologically. The name is also applied to deopening of colour in cachectic persons.

Argyria or coloration with oxide of silver is an occasional result of the internal administration of salts of silver. The coloration oooun chiefly in parts exposed to light, and it is due to the formation of oxide of silver in a finely granular form. The silver is confined to the cutis vera, where it is in the connective tissue, more especially in the elastic-fibre and more dense membranous parts. The affected persons have a peculiar bluish colour. A local argyria has been observed in persons whose occupations exposed them to the dust of silver.

Xeroderma pigmentosum is considered further on under tumours.