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SPF - Sun Protection Factor and Sunscreen

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Updated July 03, 2010

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Definition:

SPF stands for Sun Protection Factor, which is an indication of how much protection a sunscreen offers against UVB rays and sunburn.

In general, a sunscreen with:

  • SPF 2 blocks 50 percent of UVB rays
  • SPF 4 blocks 75 percent of UVB rays
  • SPF 8 blocks 87 percent of UVB rays
  • SPF 15 blocks 93 percent of UVB rays
  • SPF 30 blocks 97 percent of UVB rays
  • SPF 50 blocks 98 percent of UVB rays
  • SPF 100 blocks 99 percent of UVB rays

While you can certainly use a sunscreen with SPF 50+ to SPF 100+, keep in mind that they don't offer that much extra protection. Using a high SPF sunscreen might be a good idea for those parents who don't use enough sunscreen and don't reapply it often enough though.

Also remember that SPF is only an indication of effectiveness against UVB rays. That is why it is important for parents to for a broad-spectrum sunscreen with at least SPF 15 to SPF 30, which should block most UVA and UVB rays when applied properly. They should avoid a low SPF sunscreen or suntan lotion, which don't provide enough sun protection.

UVA Protection Ratings

There is currently no easy way to know how effective a sunscreen is against UVA rays. New FDA sunscreen labeling, in addition to possibly placing a cap of SPF 50+, would introduce a new UVA four-star system so that parents could easily figure out if a sunscreen offered low UVA protection (one star) or the highest UVA protection (four stars).

The new labels would also clearly state if a sunscreen offered 'no UVA protection.'

SPF for Clothing

Clothing has a separate rating system that is similar to the SPF rating of sunscreen.

However, instead of an SPF rating, some clothing has a Ultraviolet Protection Factor (UPF) rating, which can range from 15 (good sun protection) to 50+ (excellent sun protection) to indicate the percentage of UVA and UVB rays it can block.

Pronunciation: S.P.F.
Also Known As: Sun Protection Factor, SPF Protection
Examples:
A sunscreen with SPF 4 does not provide enough sun protection for kids.
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