Why do we lose our tans in the winter?
(Lansing State Journal, October 18, 1995)
Melanin is produced by a specialized skin cell called a melanocyte. The melanocyte is found in the epidermis, which is the outer layer of the skin. Melanin protects against harmful effects of sunlight such as sunburn and skin cancer (melanoma). Melanocytes produce more melanin when exposed to sunlight (hence a tan).
Skin cells have very short lives. The skin that you see in the outside of your body is actually made up of dead skin cells. these dead cells form a protective barrier against the environment. The dead skin cells are constantly being worn away and replaced by the live skin cells in the inner part of the epidermis.
Melanocytes produce more melanin in the summer, because they are exposed to stronger sunlight.