Sun Tanning - Tanning Process

Tanning Process

Melanin is produced by cells called melanocytes in a process called melanogenesis. Melanocytes produce two types of melanin: pheomelanin (red) and eumelanin (very dark brown). Melanin protects the body by absorbing solar radiation. Excessive solar radiation causes direct and indirect DNA damage to the skin and the body naturally combats and seeks to repair the damage and protect the skin by creating and releasing further melanin into the skin's cells. With the production of the melanin, the skin color darkens, but the UV-B in sunlight can also cause sunburn. The tanning process can also be created by artificial UV radiation, which can be delivered as UV-A, UV-B, or a combination of both.

There are two different mechanisms involved in production of a tan by UV exposure: Firstly, UV-A radiation creates oxidative stress, which in turn oxidises existing melanin and leads to rapid darkening of the melanin. UV-A may also cause melanin to be redistributed (released from melanocytes where it is already stored), but its total quantity is unchanged. Thus, the effect of UV-A leads to skin darkening, but this is only cosmetic since it does not lead to greatly increased production of melanin and therefore also to little increase in protection against UV-B, or protection against sunburn.

In the second process, triggered primarily by UV-B, there is an increase in production of melanin (melanogenesis), which is the body's reaction to direct photodamage (formation of pyrimidine dimers) from UV radiation. Melanogenesis leads to delayed tanning, and first becomes visible about 72 hours after exposure. The tan that is created by an increased melanogenesis lasts much longer than the one that is caused by oxidation of existing melanin, and is also actually protective against UV skin damage and sunburn, rather than simply cosmetic. However, in order to cause true melanogenesis-tanning by means of UV exposure, some direct DNA photodamage must first be produced, and this requires UV-B exposure (as present in natural sunlight, or sunlamps that produce UV-B).

As noted above, the ultraviolet frequencies responsible for tanning are often divided into the UVA and UVB ranges, which will be discussed: