Sun tanning or tanning is the process whereby skin color is darkened or tanned. It is most often a result of exposure to ultraviolet (UV) radiation from sunlight or from artificial sources, such as a tanning lamp found in indoor tanning beds. People who deliberately tan their skin by exposure to the sun engage in a passive recreational activity of sun bathing. Some people use chemical products that can produce a tanning effect without exposure to ultraviolet radiation, known as sunless tanning.
Impact on skin health
Moderate exposure Moderate exposure to direct sunlight contributes to the production of melanin and vitamin D by the body.
Excessive exposure Excessive exposure to ultraviolet rays has negative health effects, including sunburn. Some people tan or sunburn more easily than others. This may be the result of different skin types and natural skin color, and these may be a result of genetics. The term "tanning" has a cultural origin, arising from the color tan. Its origin lies in the Western culture of Europe when it became fashionable for young women to seek a less pale complexion (see Cultural history below).
Long-term Excessive exposure may in the long-term increase the risk of skin cancer, as well as depressed immune system function and accelerated aging of the skin.
Tanning process
Melanin is a natural pigment 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 ultraviolet radiation. Excessive UV radiation causes sunburn along with other 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 melanin, the skin color darkens. The tanning process can be triggered by natural sunlight or by artificial UV radiation, which can be delivered in frequencies of UVA, UVB, or a combination of both. The intensity is commonly measured by the UV Index. There are two different mechanisms involved in the production of a tan by UV exposure. Firstly, UVA radiation creates oxidative stress, which in turn oxidizes existing melanin, leading to the rapid darkening of the melanin. UVA may also cause melanin to be redistributed (released from melanocytes where it is already stored), but its total quantity is unchanged. Skin darkening from UVA exposure does not lead to significantly increased production of melanin or protection against sunburn. In the second process, triggered primarily by UVB, there is an increase in production of melanin (melanogenesis), which is the body's reaction to direct DNA photodamage (formation of pyrimidine dimers) from UV radiation. Melanogenesis leads to delayed tanning, and typically becomes visible two or three days after exposure. The tan that is created by increased melanogenesis typically lasts for a few weeks or months, much longer than the tan that is caused by oxidation of existing melanin, and is also actually protective against UV skin damage and sunburn, rather than simply cosmetic. Typically, it can provide a modest Sun Protection Factor (SPF) of 3, meaning that tanned skin would tolerate up to 3 times the UV exposure as pale skin. However, in order to cause true melanogenesis-tanning by means of UV exposure, some direct DNA photodamage must first be produced, and this requires UVB exposure (as present in natural sunlight, or sunlamps that produce UVB). The ultraviolet frequencies responsible for tanning are often divided into the UVA and UVB ranges.
UVA Ultraviolet A (UVA) radiation is in the wavelength range 320 to 400 nm.
UVB Ultraviolet B (UVB) radiation is in the wavelength range 280 to 320 nm. Much of this band is blocked by the Earth's ozone layer, but some penetrates. UVB:
triggers the formation of CPD-DNA damage (direct DNA damage), which in turn induces an increased melanin production. is more likely to cause a sunburn than UVA as a result of overexposure. The mechanism for sunburn and increased melanogenesis is identical. Both are caused by the direct DNA damage (formation of CPDs). produces Vitamin D in human skin. is reduced by virtually all sunscreens in accordance with their SPF. is thought, but not proven, to cause the formation of moles and some types of skin cancer. stimulates the production of new melanin, which leads to an increase in the dark-colored pigment within a few days.
Tanning behavior of different skin colors
A person's natural skin color affects their reaction to exposure to sunlight. An individual's natural skin color can vary from a dark brown to a nearly colorless pigmentation, which may appear white. In 1975, Harvard dermatologist Thomas B. Fitzpatrick devised the Fitzpatrick scale to describe the common tanning behavior of various skin types, as follows:
Dark skin does provide some protection against the sun's ultraviolet rays, but people with dark skin are still subject to photoaging and melanoma.
Health aspects
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