ABSTRACT
Melanin pigment is produced in melanocytes in the basal layer of the epidermis. The degree of racial pigmentation does not depend on the number of melanocytes present, but on their metabolic activity and the size and shape of their melanin-producing organelles – the melanosomes. Melanin synthesis is controlled by melanocyte-stimulating hormone and is influenced by oestrogens and androgens. Excessive pigmentation is known as hyperpigmentation, and decreased pigmentation is known as hypopigmentation. There are several varieties of genetically determined defects in melanin synthesis, the most common of which is recessively inherited oculocutaneous albinism. Drugs can cause generalized diffuse hyperpigmentation, patchy generalized or localized hyperpigmentation. Transient skin discoloration is seen in methaemoglobinaemia and sulfhaemoglobinaemia due to dapsone administration. A very common type of localized hyperpigmentation is chloasma or melasma. Post-inflammatory hyperpigmentation may be due to melanocytic hyperplasia occurring as part of epidermal thickening in chronic eczema, particularly atopic eczema.
