Does a higher SPF number mean stronger sun protection?

The common way to read a sunscreen shelf is simple. A bigger SPF number buys stronger protection. The federal agency that regulates sunscreen states a version of that idea itself. On its consumer page, last updated October 16, 2026, the Food and Drug Administration says: "Higher SPF values (up to 50) provide greater sunburn protection."¹

That sentence is accurate, and it is narrower than it looks. The same page says SPF values "primarily indicate a sunscreen's UVB protection," because the number comes from a sunburn test.¹ FDA's pending proposal says that under current labeling a higher-numbered bottle may protect less against UVA than a lower-numbered one, as when an SPF 30 without a broad spectrum label is compared with a broad spectrum SPF 15.⁵ The agency also says it lacks data showing a meaningful clinical benefit above SPF 60.³ Neither position has been made binding.²

What does the number measure?

SPF is a sunburn number. FDA's consumer page explains that SPF values are set by a test that measures protection against sunburn. For that reason they primarily indicate UVB protection.¹ The page says higher values give greater sunburn protection "up to 50." It does not say how much greater, and it says nothing about values above 50.¹

I found no FDA source for the percentage often quoted with the number. The Skin Cancer Foundation, in a Q&A by Steven Q. Wang, MD, last updated June 30, 2026, says SPF 30 blocks "about 97 percent of UV rays." The page gives no citation for the figure.⁸ The same page says SPF reflects both UVB and UVA. FDA's page says SPF primarily indicates UVB.⁸,¹ I found no FDA statement of the 97 percent figure in the documents reviewed for this essay.

Can a higher number protect less?

FDA says it can. In proposed order OTC000008, signed September 24, 2021, the agency describes a situation "in which a higher numbered product (for example, one labeled SPF 30) may provide inferior protection against UVA radiation than a lower numbered product (for example, one labeled broad spectrum SPF 15)."⁵ Under the current rules, SPF mainly tracks UVB, and a product without a broad spectrum label can carry a higher SPF yet give less UVA protection than a lower-numbered broad spectrum product. The proposed fix is not in force.⁵

The American Academy of Dermatology treats these as separate criteria. Its sunscreen guidance lists broad-spectrum protection against UVA and UVB, SPF 30 or higher, and water resistance as three distinct items.⁹ That is professional-society guidance, not a regulation or a trial.⁹

Is there a ceiling?

FDA has proposed one twice. Neither proposal has been finalized. On February 26, 2019, the agency published a proposed rule at 84 FR 6204. It said: "Given the lack of data showing that sunscreens with SPF values above 60 provide additional meaningful clinical benefit, we are proposing not to allow labeled SPF values higher than 60+."³ The CARES Act replaced that rulemaking process. The 2021 proposed order carries the same positions forward.³

The 2021 order adds a measurement concern. It says the clinical evaluation used in SPF testing "creates variability that justifies the use of SPF ranges." It also says "this variability is exacerbated at high SPFs."⁴ That finding concerns how precise the test is. It is not a finding about protection outdoors.⁴

For now there is no cap. FDA's Q&A page, updated September 10, 2026, says the deemed final order created by the CARES Act "does not include a limit on maximum SPF values." A cap of SPF 60+ exists only as a proposal.²

What do the trials show above 50?

Two split-face trials found that SPF 100+ produced less sunburn than SPF 50+ in real sunlight. In the first, Williams and colleagues reported in the Journal of the American Academy of Dermatology in May 2018 on 199 adults in Vail, Colorado. Blinded investigators rated 55.3 percent of participants, 110 of 199, as more sunburned on the SPF 50+ side. They rated 5 percent, 10 of 199, as more sunburned on the SPF 100+ side. The exposure lasted a single day, at high altitude. Four of the six authors are affiliated with Johnson & Johnson Consumer Inc., which makes sunscreen. The abstract does not name a funder.⁶,⁶

In the second, Kohli and colleagues reported in the same journal in April 2020 on 55 participants at one Florida beach over 5 consecutive days. After 5 days, 31 participants, or 56 percent, had more sunburn on the SPF 50+ side. Four participants, or 7 percent, had more sunburn on the SPF 100+ side.⁷ Only 1 participant had skin phototype I. Johnson & Johnson Consumer Inc. funded the protocol, and its employees are co-authors.⁷

Both trials compare SPF 100+ with SPF 50+ and nothing else. Neither tests the step from SPF 15 to SPF 30. Neither can show that every increase in the number matters.⁶,⁷ The Williams paper was published online in December 2017 and in the May 2018 print issue, nine to fourteen months before FDA's 2019 statement that data were lacking above SPF 60. The portions of the FDA documents I read do not show how the agency weighed it.³,⁶ I read the abstracts of both trials, not the full texts.

Where does this sit in the monograph story?

Our essay of August 18, 2026 covered the permitted ingredient list and the one filter added to it this year.¹⁰ The SPF ceiling belongs to the same unfinished rewrite. As of September 10, 2026, the ceiling is still only a proposal.²