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VH Skincare Glossary

SPF (sun protection factor)

SPF, or sun protection factor, is the number on a sunscreen label that rates how well it protects against UVB rays, the main cause of sunburn.

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What it means

SPF comes from a standard laboratory test that compares the dose of UV needed to burn with and without sunscreen. SPF 30 blocks about 97 percent of UVB in that test, and SPF 50 about 98 percent.

SPF says little about UVA protection, which is why “broad spectrum” on the label matters.

Also known as

  • SPF
  • sun protection factor
  • SPF 30
  • SPF 50

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Sources

General information, not medical advice. Talk to a clinician about any decision about your health.