The Sunless Tanning Guide: 47 total pages.

against UVA rays and / or other ingredients to protect against UVB rays (more harmful for sun burning than UVA rays.) The best products offer ingredients for protection from both UVA and UVB rays. The SPF listed on the product label refers to the minimum amount of UVB sunlight required with that product in order for redness to appear on the skin after that product has been applied, versus the length of time bare skin or skin without the product applied would redden. To sum that up, the basic math involved in using the SPF number is like this. The SPF number tells people how much longer they can last out in the sun with protection for their skin without being burned. For example, say a young high school student would normally burn after 12 minutes of being out in the sun. He applies a sunscreen, also referred to as a sun block, with an SPF of 15. This means that he should be fine for 15 times his average amount of protection time. In other words, he would be protected for up to 3 hours. Here is the formula for calculating: 12 minutes x 15 SPF = 180 minutes (3 hours).

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