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Updated October 02, 2009

Definition: The SPF ("sun protection factor") listed on a bottle of sunscreen is a measure of how well the product protects your skin from the sun's shorter-wave ultraviolet B (UVB) radiation. Technically, it is the ratio of how long you could spend in the sun before burning when you're protected by sunscreen, compared to when you don't have that protection. As of 2009, SPFs can range from 2 to as much as 100 or higher. A common mistake is applying too little sunscreen, which can drastically reduce the effectiveness of the product. About 1 ounce (a palmful) of sunscreen is recommended to cover the entire body, and it should be applied half an hour before sun exposure. You should reapply every two hours if you're staying outdoors for a long period of time. Applying sunscreen properly is one of the essential recommendations to lower your risk of developing skin cancer.
Also Known As: sun protection factor
Common Misspellings: SFP
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