Tanning is a natural, temporary darkening of the skin following exposure to ultraviolet radiation, typically from sunlight. The exposure triggers an increase in the skin’s production of melanin, a dark brown to black pigment. Melanin helps protect the skin from the damaging effects of ultraviolet radiation, including sunburn. However, exposing the skin to ultraviolet radiation to promote tanning can damage and prematurely age the skin and increase the risk of skin cancer. Some people consider tanned skin attractive and actively pursue tanning despite the medical risks.
Tans range in color through various shades of brown and in tone from light to dark. The amount of darkening depends on several factors, including heredity and previous exposure to sunlight. Some people tan easily, but others tan minimally or cannot tan at all and so are highly susceptible to sunburn. Tanning is often more apparent in fair-skinned people than in people with naturally darker skin.
When exposed to sunlight for prolonged periods, the body reacts by increasing the activity of cells called melanocytes in the skin. These cells produce melanin, turning the skin darker. Melanocytes are found primarily in the outermost layer of skin, called the epidermis. The cells of the epidermis divide continuously, pushing older cells to the surface, where they are eventually shed or worn away. The shedding of melanocytes causes a tan to fade over time without continued exposure to sunlight.
The ultraviolet radiation that causes tanning is an invisible component of sunlight. Two main types of ultraviolet radiation in sunlight—known as ultraviolet A (UVA) and ultraviolet B (UVB)—affect the skin. UVB rays are more intense and are associated with sunburn. UVA rays typically cause skin to tan.
Melanin helps protect against damage by absorbing and scattering ultraviolet radiation that penetrates the skin. Melanin also absorbs unstable molecules called free radicals produced by exposure to ultraviolet radiation. Free radicals damage skin cells, causing skin to thicken, wrinkle, and show other signs of aging. Scientists know that ultraviolet radiation and free radicals also play a role in the development of skin cancer. While melanin offers some protection against these effects, tanning requires prolonged exposure to the rays that cause them.
People may use sun lamps and tanning beds to create a tan without exposing themselves to natural sunlight. Most sun lamps and tanning beds are designed to emit mainly UVA rays, reducing the risk of sunburn. However, the use of sun lamps or tanning beds does not reduce the risks of skin damage or aging or of skin cancer.
Cosmetic tanning preparations, also known as sunless tanning or self-tanning products, are commercially available as creams, lotions, or sprays. Many of these products contain dihydroxyacetone (DHA), a chemical that stains the surface layers of the skin. Such products can produce the appearance of a tan without the need for exposure to ultraviolet radiation. However, they do not necessarily provide any protection from ultraviolet radiation.
See also Skin (Skin color) ; Sun lamp ; Sunburn ; Ultraviolet rays (Harmful effects) .
