Does a high SPF really protect better than SPF 30?

SPF 30 already blocks 97% of UVB radiation, while SPF 50 blocks 98%. That one-percentage-point difference sounds small, but for people with fair skin or an elevated skin cancer risk, even that extra margin can matter. Yet a higher SPF is not a free pass: inadequate application and incomplete coverage of the UV spectrum reduce protection in practice far more than the difference between SPF 30 and SPF 50.

The SPF value on the label is, moreover, an approximation. Laboratory measurements and measurements on people correspond reasonably well for SPF 30, but the correlation is slightly less accurate for SPF 15 and SPF 50. What is printed on the packaging is therefore not the same as a precisely measured figure. The same applies, incidentally, to the distinction between 'cosmetic' and 'medical': four tested products with different labels showed comparable filter performance. A more expensive or medically labelled product is therefore not necessarily better.

Another point to bear in mind: sunscreen bought online. In a small sample, two products turned out to be completely fake, with a measured protection factor of 1, as if nothing had been applied at all. Anyone buying online would do well to check that the product comes from a reliable retailer.

Regionally, there are large differences in preference: in Asia, 71% opt for SPF 50 or higher, while in Europe a substantial share still buys a lower SPF. That preference says nothing, however, about whether that higher SPF actually does proportionally more.