Sunburn

Woman showing sunburn on her neck and shoulders.

A sunburn is a kind of burn that happens when skin is exposed to sunlight for too long. The ultraviolet part of sunlight breaks down natural chemicals in the skin. This makes the skin become red. Sunburns stay for days or weeks.

People with lighter skin sunburn more quickly than people with darker skin. This is because of a dark pigment called melanin that protects the skin. There is more of it in dark-skinned people than in light-skinned people. Eventually, if exposed to too much sunlight, skin cancer may develop. In any event, sunburn can be extremely painful.

Sunburn Media

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  The cause of sunburn is the direct damage that a UVB photon can induce in DNA (left). One of the possible reactions from the excited state is the formation of a thymine-thymine cyclobutane dimer (right).

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  Erythemal dose rate at three Northern latitudes. (Divide by 25 to obtain the UV Index.) Source: NOAA.

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  A sunburned leg below the shorts line

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  Sunburn effect (as measured by the UV Index) is the product of the sunlight spectrum at the Earth's surface (radiation intensity) and the erythemal action spectrum (skin sensitivity). Long-wavelength UV is more prevalent, but each milliwatt at 295 nm produces almost 100 times more sunburn than at 315 nm.