Sunscreen or sunblock should be applied liberally as follows:
Adults should include sunscreen with a daily skin regimen, even if going outdoors for only a short time.
Apply initially 30 minutes before venturing outdoors for best results. (This allows time for the sunscreen to be absorbed. Then reapply every 15 to 30 minutes while in the sunlight.)
Also reapply each time after exercise or swimming. (Choose a waterproof or water-resistant formula even if activities don’t include swimming. Waterproof formulas last for about 40 minutes in the water, whereas water-resistant formulas last half as long.)
Apply a large amount (equal to about one quarter of a four-ounce bottle) to all exposed areas, including ears and feet.
Insect repellents reduce sunscreen SPFs by up to one-third. Use higher SPFs and very liberal application when applying both.