Source
FDA — Sun Protection Factor (SPF)
Quick Summary
A U.S. Food and Drug Administration explainer hosted by the Center for Drug Evaluation and Research that defines what the SPF number on a sunscreen label means. It walks through SPF as a measured ratio of UVB-burn protection, the diminishing-returns relationship between SPF number and percent UVB blocked, and the role of broad-spectrum labeling in extending protection to UVA.
| Source type | regulatory |
|---|
What Studied
Not a study. This is the FDA's regulatory-authority definition page for the SPF metric. It describes how SPF is measured in controlled testing and what the resulting number does — and does not — convey about real-world sunscreen performance.
Main Findings
The page defines SPF as a measure of how much UVB radiation it takes to redden sunscreen-protected skin compared with unprotected skin. It states that SPF 15 blocks about 93% of UVB, SPF 30 about 97%, and SPF 50 about 98%, so the gain from raising SPF flattens fast. It clarifies that SPF measures UVB-burn protection only, and that "broad-spectrum" is the label cue indicating UVA coverage.
Why It Matters
This is the regulator-issued definition of the SPF number itself. For a Question explaining what SPF to wear every day, it provides the precise framing for "SPF 30 vs SPF 50 — what's the difference?" and for the broader point that the broad-spectrum label cue does more daily-wear work than chasing the highest SPF number.
Original Source
U.S. Food and Drug Administration. "Sun Protection Factor (SPF)."
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- Source
- FDA — Sun Protection Factor (SPF)
- Quick Summary
- A U.S. Food and Drug Administration explainer hosted by the Center for Drug Evaluation and Research that defines what the SPF number on a sunscreen label means. It walks through SPF as a measured ratio of UVB-burn protection, the diminishing-returns relationship between SPF number and percent UVB blocked, and the role of broad-spectrum labeling in extending protection to UVA.
- What Studied
- Not a study. This is the FDA's regulatory-authority definition page for the SPF metric. It describes how SPF is measured in controlled testing and what the resulting number does — and does not — convey about real-world sunscreen performance.
- Main Findings
- The page defines SPF as a measure of how much UVB radiation it takes to redden sunscreen-protected skin compared with unprotected skin. It states that SPF 15 blocks about 93% of UVB, SPF 30 about 97%, and SPF 50 about 98%, so the gain from raising SPF flattens fast. It clarifies that SPF measures UVB-burn protection only, and that "broad-spectrum" is the label cue indicating UVA coverage.
- Why It Matters
- This is the regulator-issued definition of the SPF number itself. For a Question explaining what SPF to wear every day, it provides the precise framing for "SPF 30 vs SPF 50 — what's the difference?" and for the broader point that the broad-spectrum label cue does more daily-wear work than chasing the highest SPF number.
- Supports
- question_what-spf-should-i-use-every-day, concern_sun-damage, ingredient_zinc-oxide, ingredient_titanium-dioxide, ingredient_avobenzone, side_effect_photoallergic-contact-dermatitis-uv-filters, product_eltamd-uv-clear-spf-46