Is SPF 100 better than SPF 50?

Is SPF 100 better than SPF 50? #askdrnatalia

According to a fairly recent clinical trial published in the Journal of the American Academy of Dermatology, SPF 100 is indeed better at protecting from sunburn than SPF 50. Williams et al (2018) performed a high-quality clinical trial in 199 participants. This was a split-face design so each person used either SPF 50 or 100 on each side of their face. Both sunscreens were standard ‘big brand’ broad-spectrum inexpensive chemical sunscreens that are easily available in most countries.

They had the participants apply their sunscreen and then spend an average of 6 hours out skiing in Vail, Colorado. The next day they were examined to see which side of their face got more sunburnt. The investigators found that over 40% of participants where sunburned on the SPF 50 side compared to 13% on the SPF 100 side, which was statistically significant.

The participants weren’t even very good at putting on the sunscreen, despite getting clear instructions: they applied only half the amount of sunscreen required to reach the stated SPF (it’s 2 mg/cm2) and more than 70% of the participants reported 1 or fewer reapplications over a 6 hour period. My question is – if they had applied the correct volume of sunscreen, would the SPF 50 group still have gotten sunburnt? And would the SPF 100 group not get sunburnt at all?

Considering the fact that most people use nowhere near enough sunscreen volume to achieve the stated SPF, should we all opt for SPF 100? Based on this study, I would say ‘probably yes’ – this is an example of a well-done superiority trial so I think the results are valid and should be reproducible.