Sunscreen is one of your best defenses against UVA and UVB rays. The American Academy of Dermatology recommends sticking to a water-resistant, broad-spectrum protection with SPF 30 or higher. But if you're still getting burned, you should take it up to SPF 50, says UTMB’s Dr. Erica Kelly. She also notes that you should avoid the sun during midday (when UV rays are at their strongest) and reapply sunscreen (about a shot glass amount for every exposed skin area) if you've been sweating a lot, if you've been in the water, or if you've been sitting in the sun for 80 minutes or longer. The AAD suggests reapplying after every two hours, but Kelly says you can slather it on more often if necessary.