SPF 50+ vs. SPF 100+, Explained: What the EU and US Label Caps Mean, and What Two Split-Face Sunburn Trials of 199 and 55 People Measured

What the SPF number is

SPF is a ratio: the UV dose that causes minimal redness on skin with the product, divided by the dose on bare skin. It was measured at a fixed amount, which our 2 mg/cm² guide explains. Our own arithmetic, not a study result: SPF 30 corresponds to about 1/30 (3.3%) of the redness-causing dose reaching skin, SPF 50 to 2%, and SPF 100 to 1%. That holds only at the tested amount.

Why the EU labels stop at 50+

The European Commission's 2006 Recommendation (2006/647/EC) asks for labels to use one of eight values: 6, 10, 15, 20, 25, 30, 50 and 50+. Measured SPF of 60 or more is printed as 50+, and the values sit in four bands: low, medium, high and very high. It also asks for UVA protection of at least one third of the labeled SPF and a critical wavelength of at least 370 nm.

What the US label allows

FDA's question-and-answer page says the maximum labeled SPF has been 50+ since 2011. In its proposal, the agency would raise the cap to 60+ and allow products formulated up to SPF 80, citing evidence of added benefit up to about SPF 60. The same page describes a proposed UVA I to UV ratio of at least 0.7 for broad spectrum products.

The 199-person trial

In a 2018 Journal of the American Academy of Dermatology study, Williams and colleagues had 199 adults wear SPF 100+ on one side of the face and SPF 50+ on the other in natural sunlight in Vail, Colorado, for an average of 6.1 hours. Next day, 55.3% (110 people) were judged more sunburned on the SPF 50+ side and 5% (10 people) on the SPF 100+ side. The authors note a single-day exposure as a limitation.

The five-day beach trial

A 2020 follow-up by Kohli and colleagues used 55 people over up to five consecutive days at the beach, with each person applying both products to randomized sides. After five days, 31 people (56%) had more sunburn on the SPF 50+ side and 4 (7%) on the SPF 100+ side. Only one participant had skin phototype I.

What these results do and do not show

Both abstracts compare one SPF 100+ product with one SPF 50+ product and do not name the formulas, so the number cannot be separated from filters or UVA coverage. This is our reading, not a finding: real use is usually thinner than the tested amount, so a higher number may leave more margin. Neither trial measured long-term outcomes, and sunburn is the endpoint. For the UVA side of a Korean label, see our PA rating guide.

Reading a label with this in mind

Check which cap the label follows, whether it lists a PA grade or broad spectrum wording, and how much you really apply. New filters can change formulas too, as in our bemotrizinol article. Coverage and reapplying still matter, as the UV-photography study on moisturizer order showed.

Short version

EU labels stop at 50+, the US label stops at 50+ with a 60+ proposal, and two trials favored SPF 100+ for sunburn in outdoor use. This article is educational, not medical advice. Patch-test new products, and see a dermatologist for skin concerns.