Sunscreen Ratings: SPF Significance
Sunscreens are rated by Sun Protection Factor, SPF. SPF indicates the level of protection. The higher the SPF of a sunscreen the greater the level of protection it offers.
SPF is the relative time for developing redness upon exposure to UV radiation of sunscreen applied skin versus skin without the sunscreen. In other words, SPF refers to the amount of time you can stay in the sun without burning. A SPF 15 blocks about 95% of the UV radiation while 98% by SPF 30.
It means that a sunscreen with SPF of 15 will take 15 times more time to develop redness than without it. It means that a sunscreen with SPF 15 will take 15 times more time to develop redness than without it or in other words with SPF 15 you can stay 150 minutes without burning (15 x 10 minutes) in sun if you normally burn in 10 minutes. This means that higher the SPF, better the protection from the sun.
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