May 22, 2026
An SPF 30 sunscreen filters roughly 97 percent of UVB radiation. SPF 50 gets you to about 98. Those are the numbers the US Food and Drug Administration works from, and they are the reason the labelling rules cap the claim rather than letting brands keep climbing.
One percentage point sounds like nothing, and in a single sitting it mostly is. What actually decides your outcome is quantity and reapplication. Most people apply between a quarter and half of the amount used in lab testing, which means a bottle labelled 50 is behaving like something closer to 15 on your face.
Two grams per square centimetre is the test standard. For a face and neck that works out to roughly a third of a teaspoon, which is more product than almost anyone uses.
So: use enough, use it again after two hours outdoors, and stop paying a premium for the last percentage point. The number on the bottle is the least interesting variable.