Skin Pigmentation

This shows two melanocytes in the basal layer of skin. You can also see how the prickle cells in the stratum spinosum layers, appear to have a veil of melanin over the nucleus.

Overall skin colour depends on:

  1. Carotene pigments in subcutaneous fat (adipose tissue) (orange-yellow colour).
  2. Amount of blood and how much oxygen its carrying - haemoglobin (red colour).
  3. Amount of a pigment called melanin that there is in the epidermis (brown colour).

Melanin is made by melanocytes.

Up to 8% (1 in every 5 to 10 cells) in the epidermis is a melanocyte (melano means black) make up 8% of the epidermal cells.

Melanocytes make the pigment called melanin. Tyrosine is converted into dihydroxyphenylalanine (DOPA) which is then polymerised into melanin. The melanin pigment binds to protein, and the melanoprotein is transferred along the long dendritic processes of the melanocyte in vesicles (called melanosomes). The tips of these processes are then phagocytosed by the surrounding keratinocytes, which then take up the melanin.

Melanin protects cells from damage by UV, by producing a 'veil' over the nucleus.

Melanocytes are found in the stratum basale layer. About 1 in every 5 to 10 cells in this layer is a melanocyte.

Melanocyte number is the same in all races.

In different races, the number of melanocytes is THE SAME. In light skinned people, the melanin is concentrated deep in the epidermis, particularly in the stratum basale layer. Differences in skin colour depend on how much melanin is produced, the size of the melanosomes, and the degree to which they aggregate. The amount of melanin made can be increased by increasing exposure to UV light. However, albinos cannot make this pigment.