|Sunscreens should be applied to dry skin 15 to 30 minutes BEFORE going outdoors. When using sunscreen, be sure to apply it to all exposed areas and pay particular attention to the face, ears, hands and arms. Coat the skin liberally and rub it in thoroughly — most people apply only 25 to 50 percent of the recommended amount of sunscreen.
One ounce, enough to fill a shot glass, is considered the amount needed to cover the exposed areas of the body properly. Don't forget that lips get sunburned, too, so apply a lip balm that contains sunscreen with an SPF of 30 or higher.
Sunscreens should be reapplied about every two hours, or after swimming or perspiring heavily. Even so-called "water-resistant" sunscreens may lose their effectiveness after 40 minutes in the water. Sunscreens rub off as well as wash off, so if you've towel-dried, reapply sunscreen for continued protection.
Also, there are a number of combination cosmetic products, such as moisturizers that contain sunscreen, but it is important to remember that these products also need to be reapplied to achieve continued UV protection.