If you're out on a long training run for 2-3 hours during the spring, summer, or fall, use a sweatproof sunblock to help prevent a painful sunburn the next day. Although you'll probably sweat some of it off on a hot, humid day, a sweatproof formula sunblock stands up to sweat much better than a standard formula. Many skin care manufacturers including offer sweat-resistant sunblocks at prices ranging from less than $10 a bottle to $30 or more. You don't have to spend a lot on sunblock, but make sure you use a lot. Don't forget the backs of your legs and the back of your neck.