Why does skin tan?
Skin tans because ultraviolet light from the Sun triggers skin cells called melanocytes to produce more melanin, a brown pigment that helps protect skin from UV damage.
When ultraviolet radiation reaches the skin, it can damage the DNA in skin cells. In response, melanocytes increase production of melanin and pass it to surrounding skin cells, where it forms a protective shield over the cell nucleus. This darkening is a sign that the skin has already been damaged.
There are two stages of tanning. Immediate darkening happens within minutes to hours as existing melanin changes. Delayed tanning appears a few days later as new melanin is produced. A tan offers only limited protection, roughly equal to a low-strength sunscreen.
Sun safety
Too much UV exposure causes sunburn, premature skin aging and skin cancer, including melanoma. Health experts recommend sunscreen, protective clothing, hats, sunglasses and shade during the strongest sun, usually from late morning to mid-afternoon. Tanning beds also increase skin cancer risk.
Did You Know?
Some self-tanning products contain a sugar called dihydroxyacetone, which reacts with proteins in the skin's surface to create a temporary brown color without UV.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.