Quote Originally Posted by Grog View Post
Dermatologist-father-in-law suggested to me a while ago that using anything above SPF 30 was pretty much useless, but I am afraid I have not quite understood the reason why (I'll ask later). Repeating application seemed to be more efficient in his view...

Maybe high SPF gives us a false sense of sun-safety...
The SPF number really refers to how long a time period it protects you for. An spf of 15 needs to be reapplied more often, but it protects you just as much as an spf of 40. The 40 will simply last longer before repplying is needed.