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Monday June 6 2011 8:00 pm
http://en.wikipedia.org/wiki/Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet (UV) radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV radiation can be life-threatening in extreme cases. Exposure of the skin to lesser amounts of UV radiation will often produce a suntan. Excessive UV radiation is the leading cause of primarily non-malignant skin tumors. Sunscreen is widely agreed to prevent sunburn, although some scientists argue that it may not effectively protect against malignant melanoma, which either is caused by a different part of the ultraviolet spectrum or is not caused by sun exposure at all. Clothing, including hats, is considered the preferred skin protection method. Moderate sun tanning without burning can also prevent subsequent sunburn, as it increases the amount of melanin, a skin photoprotectant pigment that is the skin's natural defense against overexposure. Importantly, both sunburn and the increase in melanin production are triggered by direct DNA damage. When the skin cells' DNA is damaged by UV radiation, type I cell-death is triggered and the skin is replaced. Malignant melanoma may occur as a result of indirect DNA damage if the damage is not properly repaired. Proper repair occurs in the majority of DNA damage. The only cure for sunburn is slow healing, although some skin creams can help with the symptoms. Sunburn is caused by UV radiation, either from the sun or from artificial sources, such as welding arcs, the lamps used in sunbeds, and ultraviolet germicidal irradiation. It is a reaction of the body to the direct DNA damage, which can result from the excitation of DNA by UV-B light. This damage is mainly the formation of a thymine dimer. The damage is recognized by the body, which then triggers several defense mechanisms, including DNA repair to revert the damage and increased melanin production to prevent future damage. Melanin transforms UV-photons quickly into harmless amounts of heat without generating free radicals, and is therefore an excellent photoprotectant against direct and indirect DNA damage. It has been shown that protection against sunburn with chemical sunscreens does not imply protection against other damaging effects of UV radiation. Ultraviolet B (UVB) radiation causes dangerous sunburns and increases the risk of two types of skin cancer: basal-cell carcinoma and squamous cell carcinoma. The statement sunburn causes skin cancer is accurate when it refers to either basal-cell carcinoma, the mildest form of cancer, or squamous cell carcinoma. But the statement is false when it comes to malignant melanoma (see picture: UVR sunburn melanoma). The statistical correlation between sunburn and melanoma is due to a common cause — UV radiation. However, they are generated via two different mechanisms: Direct DNA damage is ascribed by many medical doctors to a change in behaviour of the sunscreen user due to a false sense of security afforded by the sunscreen. (Other researchers blame insufficient correction for confounding factors; light-skinned individuals versus indirect DNA damage. )Topically applied sunscreen blocks UV rays as long as it does not penetrate into the skin. This prevents sunburn, suntanning, and skin cancer. If the sunscreen filter is absorbed into the skin, it prevents sunburn, but increases the amount of free radicals, which in turn increases the risk for malignant melanoma. The harmful effect of photo-excited sunscreen filters on living tissue has been shown in many photo-biological studies. Whether sunscreen prevents or promotes the development of melanoma depends on the relative importance of the protective effect from the topical sunscreen versus the harmful effects of the absorbed sunscreen. The use of sunscreen is known to prevent the direct DNA damage that causes sunburn and the two most common for
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5:25
Sun Safety - Spotting skin cancer (5min 25sec)by canadiandermatology68,837 views
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