tanning là gì

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Sun tanning or tanning is the process whereby skin color is darkened or tanned. It is most often a result of exposure to tát 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 tát the sun engage in a passive recreational activity of sun bathing. Some people use chemical products which can produce a tanning effect without exposure to tát ultraviolet radiation, known as sunless tanning.

Impact on skin health[edit]

Moderate exposure[edit]

Moderate exposure to tát direct sunlight contributes to tát the production of melanin and Vi-Ta-Min D by the body toàn thân.

Excessive exposure[edit]

Excessive exposure to tát ultraviolet rays has negative health effects, including sunburn. Some people tan or sunburn more easily than thở others. This may be the result of different skin types and natural skin color, and these may be a result of genetics.^[1][2] 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 tát seek a less pale complexion (see Cultural history below).

Long-term[edit]

Excessive exposure may in the long-term increase the risk of skin cancer,^[3] as well as depressed immune system function and accelerated aging of the skin.^[4]

Tanning process[edit]

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 toàn thân by absorbing ultraviolet radiation. Excessive UV radiation causes sunburn along with other direct and indirect DNA damage to tát the skin, and the body toàn thân naturally combats and seeks to tát 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. 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.^[5] The intensity is commonly measured by the UV Index.^[6]

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 and leads to tát rapid darkening of the melanin. UVA may also cause melanin to tát 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 tát significantly increased production of melanin or protection against sunburn.^[7] In the second process, triggered primarily by UVB, there is an increase in production of melanin (melanogenesis),^[8] which is the body's reaction to tát direct DNA photodamage (formation of pyrimidine dimers) from UV radiation.^[9] Melanogenesis leads to tát delayed tanning, and typically becomes visible two or three days after exposure.^[8] The tan that is created by increased melanogenesis typically lasts for a few weeks or months, much longer than thở the tan that is caused by oxidation of existing melanin, and is also actually protective against UV skin damage and sunburn, rather than thở simply cosmetic. Typically, it can provide a modest Sun Protection Factor (SPF) of 3, meaning that tanned skin would tolerate up to tát 3 times the UV exposure as pale skin.^[10] However, in order to tát 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).^{[citation needed]} The ultraviolet frequencies responsible for tanning are often divided into the UVA and UVB ranges.

UVA[edit]

Ultraviolet A (UVA) radiation is in the wavelength range 320 to tát 400 nm.^[11] It is present more uniformly throughout the day, and throughout the year, than thở UVB. Most UVA is not blocked by the atmosphere's ozone layer. UVA causes the release of existing melanin from the melanocytes to tát combine with oxygen (oxidize) to tát create the actual tan color in the skin.^{[citation needed]} UVA is blocked less than thở UVB by many sunscreens, but is blocked to tát some degree by clothing. UVA is known both to tát cause DNA damage and to tát be carcinogenic. However, it operates not by inducing direct DNA damage, but by producing reactive oxygen species which damage DNA indirectly. UVA (see above) induces a cosmetic tan but little extra melanin protection against sun damage, sun burn, or cancer.^{[citation needed]}

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UVB[edit]

Ultraviolet B (UVB) radiation is in the wavelength range 280 to tát 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.^[9]
• is more likely to tát cause a sunburn than thở UVA as a result of overexposure. The mechanism for sunburn and increased melanogenesis is identical.^[12] 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 tát cause the formation of moles and some types of skin cancer.
• causes skin aging (but at a slower rate than thở UVA).^{[citation needed]}
• stimulates the production of new melanin, which leads to tát an increase in the dark-colored pigment within a few days.^[13]

Tanning behavior of different skin colors[edit]

A person's natural skin color affects their reaction to tát exposure to tát sunlight. An individual's natural skin color can vary from a dark brown to tát a nearly colorless pigmentation, which may appear white. In 1975, Harvard dermatologist Thomas B. Fitzpatrick devised the Fitzpatrick scale which described the common tanning behavior of various skin types, as follows:^[14][15]

Health aspects[edit]

The most common risk of exposure to tát ultraviolet radiation is sunburn, the tốc độ and severity of which vary among individuals. This can be alleviated at least to tát some extent by the prior application of a suitable-strength sunscreen, which will also hinder the tanning process due to tát the blocking of UV light. Overexposure to tát ultraviolet radiation is known to tát cause skin cancer,^[16] make skin age and wrinkle faster,^[17] mutate DNA,^[18] and impair the immune system.^[19] Frequent tanning bed use triples the risk of developing melanoma, the deadliest size of skin cancer, according to tát a 2010 study. The study suggests that the melanoma risk is linked more closely to tát total exposure than thở it is to tát the age at which an individual first uses a tanning bed.^[20] The International Agency for Research on Cancer places the use of tanning beds in the highest cancer risk category, describing them as carcinogenic to tát humans even if used as recommended.^{[citation needed]} Frequent tanning also has behavioural reinforcing effects,^[21] following UVA radiation epidermal keratinocytes synthesize POMC inducing the production of β-Endorphins which are opioid agonists. An opioid blockade will also then cause withdrawal signs after habitual UV exposure leading to tát many tanners meeting the DSM-IV criteria for addiction.^[22] Several organizations, such as the World Health Organization (WHO), the American Cancer Society and the US Surgeon General have issued guidelines warning about sun tanning and UV radiation exposure, either from the sun or from indoor tanning.^[23][24][25] Production of Vi-Ta-Min D is essential for human health. Moderate exposure (avoiding sunburn) to tát UV radiation provides benefits such as increased Vi-Ta-Min D, as well as other possible benefits that are still being studied.^[26] Several tanning activators have used different forms of psoralen, which are known to tát be photocarcinogenic.^[27][28][29] Health authorities have banned psoralen since July 1996.^[30]

Cultural history[edit]

Tanning has gone in and out of fashion. In the United States and Western Europe before the 1920s, tanned skin was associated with the lower classes because they worked outdoors and were exposed to tát the sunlight. Women in particular went to tát great lengths to tát preserve pale skin, as a sign of their "refinement".^[31] Women's outdoor clothing styles were tailored to tát protect them against sunlight exposure, with full-length sleeves, and sunbonnets and other large hats, headscarves, and parasols shielding the head. Lead-^[32] and arsenic-based cosmetics were used to tát artificially whiten the skin. The preference for fair skin continued until the kết thúc of the Victorian era.^[33] By the early 20th century, the therapeutic benefits of sunlight began to tát be recognized.^[34] In 1903, Niels Finsen was awarded the Nobel Prize in Medicine for his “Finsen Light Therapy”.^[35] The therapy was a cure for diseases such as lupus vulgaris and rickets. Vitamin D deficiency was found to tát be a cause of rickets, and exposure to tát sunlight would allow Vi-Ta-Min D to tát be produced in a person. Therefore, sunlight exposure was a remedy to tát curing several diseases, especially rickets. In 1910 a scientific expedition went to tát the island of Tenerife to tát test the wider health benefits of "heliotherapy",^[36] and by 1913 "sunbathing" was referred to tát as a desirable activity for the leisured class.^[37] Shortly thereafter, in the 1920s, fashion-designer Coco Chanel accidentally got sunburnt while visiting the French Riviera. When she arrived home page, she arrived with a sun tan and her fans apparently liked the look and started to tát adopt darker skin tones themselves. Tanned skin became a trend partly because of Coco's status and the longing for her lifestyle by other members of society. In addition, Parisians fell in love with Josephine Baker, a "caramel-skinned" singer in Paris, and idolized her dark skin. These two women were leading figures of the transformation that tanned skin underwent, in which it became perceived as fashionable, healthy, and luxurious.^[38][39][40] Jean Patou capitalized on the new tanning fad, launching the first sun tan oil "Huile de Chaldee" in 1927.^[41] Just before the 1930s, sunlight therapy became a popularly subscribed cure for almost every ailment from simple fatigue to tát tuberculosis. In the 1940s, advertisements started appearing in women's magazines which encouraged sunbathing. At the same time, swimsuits' skin coverage began decreasing, with the nội y radically changing swimsuit style after it made its appearance in 1946. In the 1950s, many people used baby oil as a method to tát increase tanning. The first self-tanner came about in the same decade and was known as "Man-Tan", although it often led to tát undesirable orange skin.^[42] Coppertone, in 1953, marketed its sunscreen with a drawing of a little blond girl and her cocker spaniel tugging on her bathing suit bottom, revealing her bare bottom and tan line; this advertisement was modified around the turn of the 21st century and now shows a little girl wearing a one-piece bathing suit or shorts.^[43] In the latter part of the 1950s, silver metallic reflectors were common to tát enhance one’s tan.^{[citation needed]} In 1962, sunscreen commenced to tát be SPF rated, although SPF labeling in the US was not standardized by the FDA until 1978. In 1971, Mattel introduced Malibu Barbie, which had tanned skin, sunglasses, and her very own bottle of sun tanning lotion.^{[citation needed]} In 1978, both sunscreen with an SPF 15 rating as well as tanning beds first appeared. In 2007, there were an estimated 50,000 outlets for indoor tanning; it was a five-billion-dollar industry in the United States,^[44] and had spawned an auxiliary industry for indoor tanning lotions including bronzers, intensifiers, and accelerators. Since then, the indoor tanning industry has become more constrained by health regulations.^[45] In Trung Quốc, darker skin is still considered by many to tát be the mark of the lower classes. As recently as 2012, in some parts of Trung Quốc, ski masks were becoming popular items to tát wear at the beach in order to tát protect the wearer's face from the effects of sunlight.^[46] A 1969 innovation is tan-through swimwear, which uses fabric perforated with thousands of micro holes that are nearly invisible to tát the naked eye, but which transmit enough sunlight to tát approach an all-over tan, especially if the fabric is stretched taut. Tan-through swimwear typically allows more than thở one-third of UV rays to tát pass through (equivalent to tát SPF 3 or less), and an application of sunscreen even to tát the covered area is recommended.^[47][48][49]

Sunless tanning[edit]

To avoid exposure to tát UVB and UVA rays, or in seasons without strong sunshine, some people take alternative steps to tát appear with darkened skin. They may use sunless tanning (also known as self-tanners); stainers which are based on dihydroxyacetone (DHA);^[50] or cosmetics such as bronzers.^{[citation needed]} Many sunless tanning products are available in the size of darkening creams, gels, lotions, and sprays that are self-applied on the skin. There is also a professional spray-on tanning option or “tanning booth” that is offered by spas, salons, and tanning businesses.^[51] Spray tanning does not involve a color being sprayed on the body toàn thân, instead it uses a colorless chemical which reacts with proteins in the top layer of the skin, resulting in a brown color.^{[citation needed]}

See also[edit]

• Sunburn
• Sunning
• Indoor tanning
• Perineum sunning
• Skin whitening

References[edit]

External links[edit]

• Aim at Melanoma
• Information on tanning from The Skin Cancer Foundation
• Research on the benefits of UV exposure
• Melanoma Research Alliance