---
title: FDA — Sun Protection Factor (SPF)
entity_type: Source
canonical_url: https://skinknowledgebase.com/sources/fda-sun-protection-factor
date_modified: 2026-05-09
date_reviewed: 2026-05-09
mcp_eligible: true
source_type: regulatory
original_source_url: https://www.fda.gov/about-fda/center-drug-evaluation-and-research-cder/sun-protection-factor-spf
evidence_sources: []
product_fact_sources: []
---

# 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.

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- [What SPF should I use every day?](https://skinknowledgebase.com/questions/what-spf-should-i-use-every-day)
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