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The skin is divided into two main layers. The outer layer is known as the epidermis and the layer underneath is known as the dermis.
The skin has many purposes. It:
The epidermis contains three types of cell. On the surface are flat cells, known as squamous cells. Under the layer of squamous cells are rounder cells called basal cells. In between the basal cells are melanocytes.
Melanocytes are cells that produce a pigment called melanin. Melanin is responsible for the natural colour of our skin and protects it from the harmful effects of the sun. When the skin is exposed to sunlight, our melanocytes increase the amount of melanin to absorb more potentially harmful ultraviolet (UV) rays. This makes the skin darker and gives it a suntanned appearance. A suntan is a sign that the skin is trying to protect itself.
If you have naturally darker (brown or black) skin, you have the same number of melanocytes as people with white skin, but make more melanin. This means you have more natural protection from UV rays.
Moles (sometimes called naevi) are a group or cluster of melanocytes that are close together. Most people with white skin have about 10-50 moles on their skin. Some young adults can have as many as 100.
Content last reviewed: 1 February 2012
Next planned review: 2014
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