I, like just about everyone I have talked to about this, was under a false assumption about the SPF. I think that most people assume, like I did, that the higher the SPF number, the more protection you get; SPF 40 protects 4 times more than SPF 10. Well if you paid close attention to the above writeup you will notice that SPF is all about time. SPF 10 and 40 protect you the same amount, but the 40 does it longer. This is crucial information for someone like me who burns from little more than watching an episode of Baywatch.