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Sunscreen smarts: What's your SPF IQ?
By Mayo Clinic staff
SPF stands for sun protection factor. The SPF number is a measurement of the amount of UVB protection a sunscreen offers. The higher the number, the greater the protection. SPF is not an indication of how much time you can spend in the sun. If you use a sunscreen with an SPF of 30 rather than one with an SPF of 15, it doesn't mean you can stay in the sun twice as long. In reality, an SPF of 15 filters out about 93 percent of the UVB rays; SPF 30 filters about 97 percent of UVB rays.
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