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How does sunscreen block harmful UV rays from reaching the skin?
Question Date: 2010-04-11
Answer 1:

Sunscreens work by absorbing and/or deflecting UV rays before it reaches your skin.

The sunscreen contains chemicals that actually absorb the rays and then scatter them. This means that the length of the rays are altered enough to prevent serious damage to the skin

Another important factor that needs to be discussed when defining how sunscreens work is the Sun Protection Factor, or SPF. Everyone has an innate amount of Sun Protection Factor, or time that they may stay in the sun without burning. The SPF applies to UVB rays only, since those are the rays that cause sunburn. SPF works through multiplication. For instance, if you use a sunscreen that has an SPF of 15, then you would multiply your own natural SPF by 40 to determine how many minutes you could stay in the sun without burning. If your own SPF were 10, then that would convert to 150 minutes, or 2 hours.

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