The skin is the body’s outer protective cover. It is made up of 3 layers – epidermis, dermis and fat. The most superficial layer is called the epidermis.

The skin defends itself from UV radiation through thickening of the outer epidermis – the keratin layer. The living cells produced by the lower levels of the epidermis are slowly pushed to the surface. Cells, when they reach the surface, have become harder and drier and contain keratin, a substance which helps protect us from heat and cold.

The epidermis also contains specialist cells called melanocytes. These produce the dark skin pigment called melanin, which gives our skin some protection from burning. This production of melanin in response to trauma from UV radiation appears as a ‘tan’.

Now we can understand the origins of the word ‘tan’ – thickened and darkened skin – leather like. A “sun tan” indicates sun damage.


Moles occur where melanocytes clump together. They are usually oval or round pigmented spots, with a smooth border and regular color. They may be hard or raised and clump together. 20 to 40 are the average number of moles for an adult. Most appear around puberty, in later life many may disappear.


Freckles are flat and usually occur on sun exposed areas. Moles and freckles are very common in fair-skinned people.