Quote Originally Posted by Lisa S.H. View Post
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.
After thinking about it on my way to work (in the beautiful sun, at last), I think his point was that the higher SPFs will not hold on to the skin long enough to be efficient anyway, no matter how waterproof or sweatproof they pretend to be.

Hence the "reapply" advice.