Science Fair Project Encyclopedia
A sunburn is a radiation burn to the skin produced by overexposure to ultraviolet (UV) light, commonly from the sun's rays. A similar burn can be produced by overexposure to other sources of UV, such as tanning lamps and welding arcs. Exposure of the skin to lesser amounts of UV will often produce a suntan.
Sunburn development and consequences
Sunburns usually develop as a result of over-exposure to sun or less commonly, occupational exposure.
Sunburn occurs when exposure to UV light exceeds the protective capacity of an individual's melanin. Melanin content varies greatly but in general darker skinned people have more melanin than lighter skinned. This leads to a reduced incidence of sunburn amongst dark-skinned individuals.
Ultraviolet radiation is divided into UVA, UVB and UVC subtypes. Ozone in the Earth's atmosphere filters out some UV radiation. UVC is almost entirely eliminated by the atmosphere, but enough UVA and UVB remain that sunburn can occur in less than 15 minutes.  UVB was thought to be the causative agent in skin cancer, but there is a growing body of evidence to support the theory that both UVA and UVB cause skin cancer.
Sunburn is usually not immediately obvious. After being burnt, 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 the incident. Skin peeling begins 3 to 8 days after the burn occurs. Common outcomes include tenderness, pain, oedema, red and/or peeling skin, rash, nausea and fever. 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 admission.
The major danger of sunburn is the increased risk of future skin cancer. At the cellular level, UV 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. All sunburns result in permanent and irreversible damage. One incident of blistering sunburn doubles the risk of malignant melanoma.
The worsening danger
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 lead to dangerously high levels of UV light.
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.
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.
Sunscreen should have a SPF rating of at least 15 and sunblock should be applied half an hour before going out and reapplied every two hours thereafter.
It is also important to remember that eyes should not be neglected and that wrap-around sunglasses which block UV light should also be worn. UV light has been implicated in pterigium and cataract development.
When one is exposed to any artificial source of occupational UV, special protective clothing (for example, welding masks ) should be worn.
On cold days, people often refer to their sunburn as a windburn. Windburn is actually a distinct condition whereby the top layer of oil is removed from the skin, causing excessive dryness that leads to redness and a burning feeling. However, people commonly believe that any burn on a cold day is windburn. In fact, since sunburn is a result of UV light, not heat, hot temperatures are not necessary. This mistake is frequently made while skiing, where sunburn can occur in very cold temperatures since the UV light is reflecting off the snow and higher altitudes provide less atmosphere to block UV.
- Sun Protection Tips
- Protecting Kids from the Sun
- Sunburn Information
- Sunburn Pictures
- Medline - Sunburn
- Medline - Sunburn First Aid
- Sunsmart Victoria (Australia)
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.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details