There are many factors that influence skin colouration, including characteristics relating to superficial
microcirculation, oxygenation of the blood and diet. The pigmentation of darker and lighter skin is, however, mainly determined by the type and distribution of melanin pigments, and does not depend on the quantity of melanocytes.
Melanocytes are nerve cells located between the cells of the stratum basale of theepidermis, at the junction between the epidermis and the dermis. They synthesise melanin from tyrosine amino acid forming granules called melanosomes. The melanosomes are transferred to other epithelial cells of the epidermis through branched extensions of the cytoplasm. Once they reach the keratocytes , the melanin place themselves above the nucleus to defend it. Melanin is in fact a dark pigment which protects of the skin from the detrimental ultraviolet radiation present in sunlight . The keratocytes are therefore the epidermis cells which give the typical dark colour to the skin following exposure to the sun.
There are frequent changes in skin colour that lead to discolouration. It may manifest in the form of increased skin colouration, or HYPERPIGMENTATION, or a loss of tone, or HYPOPIGMENTATION.