Apply sunscreen about a half hour before being in the sun.

Apply sunscreen on 20 to 30 minutes before heading outside to give the ingredients time to start working. Allowing your sunscreen to soak in thoroughly and dry on the surface with help it to last longer. Swimming before your sunscreen is dry will most likely wash it right off, rendering it ineffective. Young children are often too excited to wait to have sunscreen applied once you get to the beach, so it definitely a good idea to apply their first application at home so it can soak in and dry while you are traveling to the beach or pool.