Sunburn

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Sunburn

A sunburn is a burn to the skin produced by overexposure to ultraviolet (UV) radiation, commonly from the sun's rays. A similar burn can be produced by overexposure to other sources of UV such as from tanning lamps, or occupationally, such as from welding arcs. Exposure of the skin to lesser amounts of UV will often produce a suntan. Usual mild symptoms are red or reddish skin that's hot to the touch, a washed out feeling, and mild dizziness.

Sunburn can be life-threatening and is a leading cause of cancer. Sunburn can easily be prevented through the use of sunscreen, clothing (and hats), and by limiting solar exposure, especially during the middle of the day. The only cure for skin burn is slow healing, although skin creams can help.

In the winter time, windburn is commonly confused with a sunburn, with typically milder symptoms.

Development and consequences

Typically there is initial redness (erythema), followed by varying degrees of pain, both proportional in severity to the duration and intensity of exposure. The condition occurs when incident UV radiation exceeds the protective capacity of melanin in the skin. Concentrations of this pigment vary greatly among individuals, but in general, darker-skinned people have more melanin than those with lighter skin. Correspondingly, the incidence of sunburn among dark-skinned individuals is lower.

UV radiation is divided into the UVA (380–315 nm), UVB (315–280 nm) and UVC (280-180 nm) sub-bands. Ozone in the Earth's atmosphere filters out a portion of this before it reaches the planet's surface. UVC is almost entirely eliminated by the atmosphere, but enough UVA and UVB penetrates it that sunburn can occur in less than 15 minutes. ^*

Nevertheless, the inflicted harm is often not immediately obvious. After being burned, skin may turn red 2 to 6 hours later. Pain is worst 6 to 48 hours afterward. The burn continues to develop for 24 to 72 hours after exposure. Skin peeling begins 3 to 8 days after the burn occurs. Common outcomes include tenderness, pain, edema, red and/or peeling skin, rash, nausea and fever. Also, a small amount of heat is given off from the burn, giving a warm feeling to the affected area. Sunburns may be first- or second-degree burns.

Minor sunburns typically cause nothing more than slight redness and tenderness to the affected area. In more serious cases blistering can occur. Extreme sunburns can be painful to the point of debilitation and may require hospital care.

With respect to the spectral components of sunlight, the severity of sunburn has been found to peak in the low-frequency UVB range near the 320 nm transition to UVA. This is based on two factors:

erythemal activity - the specific effect of different wavelengths of radiation on the skin
solar irradiance - how much of any solar radiation wavelength can be expected to be incident on the surface of the earth

Source: NOAA

The resulting erythemal irradiance metric is calculated by weighting measurements of solar irradiance with experimental measurements of erythemal activity. When this product is graphed, there is a peak at 308 nm.

At the cellular level, UVB light causes DNA damage which may be passed onto subsequent generations of a cell's progeny, leading to increased risk of skin cancer. Damaged cells die and release toxins which are responsible for nausea and fever. If many die, peeling may result.

The more critical and long-term danger posed by sunburn is an increased risk of future skin cancer, which is believed to be highly correlated. One incident of blistering sunburn doubles the risk of malignant melanoma. But while sunburn severity gives an indication of short-term radiation over-exposure, there is also deeper penetration by UVA that occurs in the absence of perceptible symptoms. UVB was thought to be the sole causative agent in skin cancer, but there is a growing body of evidence to support the theory that both UVA and UVB are implicated.

Increased risk

NOAA_UV-Rad_DiurnalErythemalDoseRatePerLatitude.GIF|thumb|right|Erythemal dose at three Northern latitudes
source: NOAA]] The risk of sunburn increases with proximity to the earth's equator. It can also be increased by pharmaceutical products that sensitise some users to UV radiation. Certain antibiotics, contraceptives, and tranquillizers have this effect. People with red hair and/or freckles generally have a greater risk of sunburn than others because of their lighter skin tone.

Suntans, which naturally develop in some individuals as a protective mechanism against the sun, are viewed by many in the Western world as desirable. This has led to increases in sunburn incidences and in solarium popularity as individuals attempt to tan.

In recent years, the incidence and severity of sunburn has increased worldwide, especially in the southern hemisphere, because of damage to the ozone layer due to CFCs. Some are worried that ozone depletion and the seasonal ozone hole has led to dangerously high levels of UV radiation.

A 2003 study found that 36% of US adults have a sunburn at least once a year; one study found 50% of Canadians to have been burnt in the two months prior to the study.

Protection

Skin

It is advisable to consult a UV index to determine what level of protection is necessary. Potential forms of protection include wearing long-sleeved garments and wide-brimmed hats, and using an umbrella when in the sun. Minimisation of sun exposure between the hours of 10 a.m. to 3 p.m. is also recommended.

Commercial preparations are available that block UV light, known as sunscreens. Sometimes called suncreams or sunblocks, they have a Sun Protection Factor (SPF) rating, based on the sunblock's ability to reduce the UVB radiation at the skin: the higher the SPF rating, the greater the protection. A sunscreen rated SPF15 blocks 93.3% UVB and an SPF30 rated sunscreen blocks 96.7%. It is best to use a broad spectrum sunscreen in order to protect against both UVA and UVB radiation. It is prudent to use waterproof formulations if one plans to engage in water-based activities. It should be noted that the best sunscreens attenuate UVA radiation as well UVB. Note that the stated protection factors are only correct if 2 μl of sunscreen is applied per square cm of exposed skin. This translates into about 28 ml (1 oz) to cover the whole body of an adult male, which is much more than many people use in practice.

Contrary to the common advice that sunscreen should be reapplied every 2—3 hours, research has shown that the best protection is achieved by application 15 to 30 minutes before exposure, followed by one reapplication 15 to 30 minutes after the sun exposure begins. Further reapplication is only necessary after activities such as swimming, sweating, and rubbing.

When one is exposed to any artificial source of occupational UV, special protective clothing (for example, welding helmets/shields) should be worn.

Eyes

Eyes should not be neglected, and wrap-around sunglasses which block UV light should also be worn. UV light has been implicated in pterygium and cataract development.

Treatment

The best treatment for most sunburns is time. Given a few weeks, they will heal. Immediate, temporary relief can be obtained by putting a cool, wet towel over the affected area, or taking a cold bath or shower. More severe burns may be treated with burn ointments such as silvadene.

There are numerous topical skin products that are sold over-the-counter to relieve the pain of a sunburn. Many popular products contain aloe or vitamin E.

Some common household or folk remedies include application of white vinegar and apple cider vinegar, mustard, lavender oil, cold tea, yogurt, St. John's wort, tomatos, almond milk, avocado, or cucumbers to the affected area or areas. These folk remedies are largely untested, and may do more harm than good. St John's wort, for example, is known to cause photosensitivity leading to increased susceptibility to sunburns in situations that would not normally cause them (Ernst et al., 1998).

Such topical treatments aside, the pain from a sunburn can be treated with an analgesic such as acetaminophen or ibuprofen.

Peeling sunburns are usually accompanied by itching that may be uncomfortable in more severe burns. Allergy medications such as Benadryl are effective at stopping the itch.

Animals

Most animals can suffer from sunburn; however, most are protected by a layer of dense fur. Despite myths stating that only hippopotamuses and pigs can be affected by sunburn, almost all animals - even fish, given the right conditions - can suffer sunburn (though pigs and hippopotamuses are more prone due to their hairless skin producing less oil - a natural sun protector).

Even some plants, if exposed to too much sun, can burn.

External links

References

Agar N, Halliday G, Barnetson R, Ananthaswamy H, Wheeler M, Jones A. The basal layer in human squamous tumors harbors more UVA than UVB fingerprint mutations: a role for UVA in human skin carcinogenesis. Proc Natl Acad Sci. 6 Apr 2004;101(14):4954-9.

Baron E, Fourtanier A, Compan D, Medaisko C, Cooper K, Stevens S. High ultraviolet A protection affords greater immune protection confirming that ultraviolet A contributes to photoimmunosuppression in humans. J Invest Dermatol. Oct 2003;121(4):869-75.

Hall H, Saraiya M, Thompson T, Hartman A, Glanz K, Rimer B. Correlates of Sunburn Experiences Among U.S. Adults: Results of the 2000 National Health Interview Survey. Public Health Reports 2003;118.

Haywood R, Wardman P, Sanders R, Linge C. Sunscreens inadequately protect against ultraviolet-A-induced free radicals in skin: implications for skin aging and melanoma? J Invest Dermatol. Oct 2003;121(4):862-8.

NOAA UV-Index Summary with Data Graphs

Dermatology | Health risks | Sun tanning

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