Myth: there’s no extra benefit in using SPF 100 vs SPF 30.

So the conventional wisdom used to be that people gained very little additional sun protection when applying SPFs higher than 30 compared to 30 alone. However a 2018 randomized controlled trial comparing the application of SPF50 vs SPF100 to the faces of skiers out for a day at Vail Mountain Resort found that there were fewer sunburns in the areas where SPF100 was applied vs. SPF 50.

The proposed explanation is that, in real-world use, people do not apply a thick enough layer of sunscreen to achieve the labeled level of sun protection. And they often forget to reapply. So in real life if you’re going to be in a very sunny environment for an extended period of time - you are probably better off reaching for the highest level of SPF available to you to minimize your risk of a sunburn. 

Citation: Williams JD, Maitra P, Atillasoy E, Wu MM, Farberg AS, Rigel DS. SPF 100+ sunscreen is more protective against sunburn than SPF 50+ in actual use: Results of a randomized, double-blind, split-face, natural sunlight exposure clinical trial. J Am Acad Dermatol. 2018 May;78(5):902-910.e2. doi: 10.1016/j.jaad.2017.12.062. Epub 2017 Dec 29. PMID: 29291958.