Labels recommend using a "liberal" amount of sunscreen. How much is that? —C.H., Bellows Falls, Vt.

For the average adult the appropriate amount is a full palmful.That’s a little more than a teaspoon each on the chest and stomach combined, the back, and each leg; and a little more than half a teaspoon each on the head and neck combined (including the ears) and each arm. While that may seem like a lot, studies have shown that most people get only about one-fourth to one-third of the labeled Sun Protection Factor (SPF) from sunscreens because they don’t use enough. Reapply the screen every two hours and after you’ve gotten wet and dried off.