Colour of the skin is constituted by three components:
- Melanin which contributes black colour
- Haemoglobin which contributes red or blue colour depending upon its state of oxidation or reduction, and
- Keratin which contributes light yellow colour.
Melanin constitutes the chief pigment and is produced from the amino acid tyrosine by the action of a copper containing enzyme called tyrosinase. This enzyme converts tyrosine into dihydroxyphenylalanine (DOPA) which is further converted to dopaquinone by the same enzyme.
Both these reactions are oxidative processes which are stimulated by sunlight and oxidizing agents and are inhibited by reducing agents.
Later on, through a series of non-enzymatic chemical reactions, dopaquinone gets converted into melanin and gets bound to a protein molecule.
This entire reaction occurs in small inclusions called melanosomes present in specialised pigment-producing cells called melanocytes.
The melanocytes are dendritic cells located in the basal cell layer of the epidermis and transfer their pigment to the keratinizing cells of the epidermis by means of their dendritic processes. Each melanocyte supplies the melanin pigment to nearly 30 keratinocytes.
This pigment is ultimately lost along with the keratinized cells exfoliating from the surface of the skin.
Disorders of pigmentation can arise either due to a disturbance in the formation of melanin or in its loss from the skin, but occasionally, other causes such as incontinence of melanin towards the dermis in various disease process or deposition of other extraneous pigment may also be responsible for pigmentary disorders.
