Is Bigger Always Better?

Doubling SPF Doesn't Double Sun Protection

FDA Sunscreen Ratings

Higher SPF Sunscreen Provides Better Sunburn Protection

A recently published study in the Journal of American Academy of Dermatology (2020; 82: 869-77) reported benefits of using SPF 100+ sunscreen compared to SPF 50+ sunscreen. The higher strength sunscreen provided greater protection from sunburns during five days of consecutive sun exposure designed to simulate real-world vacation behavior. Even though the difference in percentage points of UVB radiation blocked is only 2% (from 97% to 99%), more than half (56%) of patients had more sunburn on the SPF 50+ side after five days compared to only 7% on the SPF 100+ side.

How come such a small difference in the percentage of UVB radiation protection translated into such a large difference in rates of sunburn? A big reason for this unexpected finding is that the way SPF is measured in the laboratory does not match how we usually apply sunscreen at the beach. The FDA recommends applying about a shot glass full (one ounce) of sunscreen to cover an average-sized adult from head to toe. Also, sunscreen should be reapplied every two hours or more frequently if swimming or sweating outside.