A sun protection factor technically provides you with 15 times your natural protection. This means if you usually begin to show a response to sun exposure in 15 minutes, SPF 15 will allow you to stay up to three and three quarter hours (15 x 15 = 225 minutes), under normal sun conditions, before seeing a response to sun exposure. The damage to the skin, after 15 minutes of sun exposure, should therefore be limited to 1/15 of the total damage that would normally occur on unprotected skin. Skin that tans easily but does not burn
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