Harmful UV rays

Tanning refers to delayed pigmentation of the skin, or melanin pigmentation. It usually becomes noticeable one to two days after exposure to the sun and gradually increases for several days persisting for weeks or months. Tanning results from an increase in the number of functions melanocytes (pigment cells) resulting in increased activity of the enzyme tyrosinase. This leads to the formation of new melanin and an increase in the number of melanin granules throughout the epidermis (2). Tanned skin need not only be considered a harmful effect as it does confer some protection for subsequent exposure to the sun, but the degree of protection is thought to be moderate and not sufficient as a sunscreen for Caucasian skin. However, there is another mechanism that may provide more protection for subsequent exposures. In addition to tanning and sunburn, thickening (or hyperplasic) of the epidermis also occurs and is thought to be a significant component of a mild sunburn reaction. A single moderate exposure to UV-B radiation is sufficient to induce 3-fold thickening in the stratum cornea that lasts one to two months. This thickening is likely to be more important than tanning for providing endogenous photoprotection for those with Caucasian skin (1).