If you are at elevated risk of developing melanoma due to family history, having precancerous growths or moles, then you might want to supersize your SPF to 50, 60 or more. But experts stress that properly applying a lower SPF - say, SPF 30 if you're going to be at the beach or pool - goes a lot further than simply upping the number on the container. Many people get burned by improperly applying sunscreen. Use at least an ounce - that would be about the amount that would fill a shot glass - and apply it all over, paying special attention to your face, hands, feet and even ears. Reapply often, especially after swimming and sweating.