Sun tanning

# Overview
Sun tanning describes a darkening of the skin (especially of fair-skinned individuals) in a natural physiological response stimulated by exposure to ultraviolet radiation from sunshine (or a sunbed).  With excess exposure to the sun, a suntanned area can also develop sunburn.

# Cause and effect
Darkening of the skin is caused by an increased release of the pigment melanin into the skin's cells after exposure to ultraviolet radiation. Melanin is produced by cells called melanocytes and protects the body from absorbing an excess of solar radiation, which can be harmful. Depending on genetics, some people can darken quickly and deeply whereas others do not darken much at all.
The ultraviolet frequencies responsible for tanning are often divided into the UVA (315 to 400nm wavelength) and UVB (280 to 315nm wavelength) ranges. UVB have higher energy than UVA waves and are therefore more damaging and more carcinogenic.

## UVB
- triggers creation and secretion of new melanin into the skin
- is thought to cause the formation of moles and some types of skin cancer (but not melanoma)
- causes skin aging (but at a far slower rate than UVA.)
- produces Vitamin D in human skin
- is more likely to cause a sunburn than UVA as a result of overexposure
- reduced by virtually all sunscreens in accordance with their SPF

## UVA
- causes release of preexisting melanin from the melanocytes
- causes the melanin to combine with oxygen (oxidize), which creates the actual tan color in the skin
- seems to cause cancer less than UVB, but causes melanoma, a far more dangerous type of skin cancer than other types
- is blocked less than UVB by many sunscreens but is blocked to some degree by clothing
- is present more uniformly throughout the day, and throughout the seasons than UVB

# Cultural history
Culturally, a suntan may be regarded as attractive, although this is susceptible to the whims of fashion. In ancient Rome, women deliberately lightened their skin with lead based cosmetics. At the time of Shakespeare, before the industrial revolution, untanned skin signified higher status, and Elizabeth I died from the white lead cosmetics; in Much Ado About Nothing, Act II, Scene I, Beatrice observes of her self-perceived unattractiveness and her consequent lack of marriage prospects:
In Europe, during much of the 18th and 19th centuries, fair, freckleless skin was considered attractive, especially in women, since tanned skin was associated with manual labour such as on a farm or in the outdoor employ of a wealthier person. Having fair skin signified that one was wealthy enough to hire other people to do manual labour. In 18th-century France, members of the royal court emphasized this point by powdering their faces to look as white as possible. As labour patterns shifted during the early 20th century, with indoor work becoming the norm, tanned skin came to be seen as a credential for membership of the leisured classes.  When famous fashion designer Coco Chanel accidentally acquired a dark tan during a vacation on the French Riviera in the 1920's, she ignited a fad among whites for tanned skin. By the 1960s, a tan's earlier social significance had been reversed and bronzed skin among whites often signified social status, wealth and health, possibly for the opposite reason.  Now that most jobs are done inside, tans among whites signify the wealth required to have the leisure time to acquire one.

# Health benefits
The skin produces vitamin D in response to sun exposure, which can be a health benefit for those with vitamin D deficiency.  In 2002, Dr. William B. Grant published an article in the claiming that 23,800 premature deaths occur in the US annually from cancer due to insufficient UVB exposures (apparently via vitamin D deficiency).  This is higher than 8,800 deaths occurred from  melanoma or squamous cell carcinoma, so the overall effect of sun tanning might be beneficial. Another research estimates that 50,00063,000 individuals in the United States and 19,000 - 25,000 in the UK die prematurely from cancer annually due to insufficient vitamin D.
Another effect of vitamin D deficiency is osteomalacia, which can result in bone pain, difficulty in weight bearing and sometimes fractures.  This work has been updated in Grant et al. 2005 and Grant and Garland, 2006
In addition, it was reported that in Spain, risk of non-melanoma skin cancer is balanced by reduced risk of 16 types of cancer 
According to a 2007 research of Islam, Gauderman, Cozen, and Mack  , sun exposure during childhood prevents multiple sclerosis later in life.
Ultraviolet radiation has other medical applications, in the treatment of skin conditions such as psoriasis and vitiligo. Sunshine is informally used as a short term way to treat or hide acne, but research shows that in the long term, acne worsens with sunlight exposure and safer treatments now exist (see phototherapy).

# Social Context
Intentionally darkening one's skin did not become a socially desirable phenomenon in the West until the mid-20th century. For centuries, sharp divisions existed in most societies between the upper classes, whose members held positions of power and leisure indoors, and the commonfolk who typically led agrarian lives toiling outside. As a result, wealthier people tended to be fairer-skinned and this correlation made pale skin more desirable. Hence, the word "fair" came to mean "beautiful". The Industrial Revolution brought poor laborers and wealthy industrialists alike inside under the same roofs and this distinction began to evaporate. By the end of World War II, the economic boom the United States experienced gave middle class citizens more time and money to devote to leisurely pursuits. Vacations became standard practice and the advent of air travel made warmer, tropical destinations a more realistic possibility for average people. Tanned skin became associated not with a hard life of labor in the fields, but with swimming pools, backyard barbecues, dinner parties, and exotic vacations. In this context, tanned skin took on a feature of attractiveness as a signal of being well-traveled, cultured, and supposed evidence of leisure wealth. It also became a signal of health and strength as the bodybuilding and fitness industries increasingly promoted tanning to highlight muscle tone and definition.
In some other parts of the world, fair skin remains the standard of beauty. The geisha of Japan were renowned for their brilliant white painted faces, and the appeal of the 

# Prevention
To avoid sunburn or excess tanning, covering up skin, wearing hats and staying out of direct sunlight is the primary defense.
If long sun exposure cannot be avoided or is desired one may use sunscreen or various over-the-counter creams to reduce sun exposure. The SPF (Sun Protection Factor) number on a sunscreen product shows its rated effectiveness. Products with a higher SPF number are those designed to provide more defense for the skin against the effects of solar radiation. However in 1998, the Annual Meeting of the American Association for the Advancement of Science reported that some sunscreens advertising UVA and UVB protection do not provide adequate safety from UVA radiation and could give sun tanners a false sense of protection.
Tanning oils or creams, when applied, are usually thicker on some parts of skin than on others.  This causes some parts of skin to get more UVA and UVB than others and thus get sunburns.  For this reason, improper application of tanning oils or creams may increase the occurrence of skin cancer and other skin diseases.
For those who choose to tan, some dermatologists recommend the following preventative measures:
- Make sure the sunscreen blocks both UVA and UVB rays. These types of sunscreens, called broad-spectrum sunscreens, contain more active ingredients. Ideally a sunscreen should also be hypoallergenic and noncomedogenic so it doesn't cause a rash or clog the pores, which can cause acne.
- Sunscreen needs to be applied thickly enough to make a difference. People often do not put on enough sunscreen to get the full SPF protection. In case of uncertainty about how much product to use, or discomfort with the amount applied, switching to a sunscreen with a higher SPF may help.
- Reapply sunscreen every 2 to 3 hours and after swimming or sweating. In direct sun, wear a sunscreen with a higher SPF (such as SPF 30). For playing sports the sunscreen should also be waterproof and sweatproof.
- The rays of the sun are strongest between 10 a.m. and 4 p.m (see ), so frequent shade breaks are recommended during these hours. Sun rays are stronger at higher elevations (mountains) and lower latitudes (near the equator). One way to deal with time zones, daylight saving time (summer time) and latitude is to check shadow length. If a person's shadow is shorter than their actual height, the risk of sunburn is much higher.
- Wear a hat with a brim and anti-UV sunglasses which can provide almost 100% protection against ultraviolet radiation entering the eyes.
- Be aware that reflective surfaces like snow and water can greatly increase the amount of UV radiation to which the skin is exposed.
The American Academy of Dermatology recommends the use of sunscreens, wearing sun protective clothing and avoiding the sun altogether.