Running outside without a hat

If you have SPF on your face and body, it might seem okay to skip wearing a hat during your morning jog. Only it's not, says Dr. Hale, an avid runner. "Sweat accelerates the speed at which sunscreen breaks down, so you might not have as much coverage as you think," she explains. Plus, you're exposing the very vulnerable skin on your scalp to the sun. "Squamous cell is correlated with chronic sun exposure rather than a day at the beach," she says.

Double your efforts with a hat and sunscreen. Choose a hat that has ultraviolet protection factor (UPF), and shield your face, neck, ears and body with a broad-spectrum SPF of at least 30. Swipe a sunscreen stick on burn-prone spots like your ears and nose. 

Anyone over the age of six months should use a sunscreen daily. Even those who work inside are exposed to ultraviolet radiation for brief periods throughout the day, especially if they work near windows, which generally filter out UVB but not UVA rays.

Children under the age of six months should not be exposed to the sun, since their skin is highly sensitive to the chemical ingredients in sunscreen as well as to the sun's rays. Shade and protective clothing are the best ways to protect infants from the sun.

How much should I use

To ensure that you get the full SPF of a sunscreen, you need to apply 1 oz - about a shot glass full. Studies show that most people apply only half to a quarter of that amount, which means the actual SPF they have on their body is lower than advertised. Sunscreens should be applied 30 minutes before sun exposure to allow the ingredients to fully bind to the skin. Reapplication of sunscreen is just as important as putting it on in the first place, so reapply the same amount every two hours. Sunscreens should also be reapplied immediately after swimming, toweling off, or sweating a great deal.

Myths

• Wearing sunscreen can cause vitamin D deficiency.

There is some controversy regarding this issue, but few dermatologists believe (and no studies have shown) that sunscreens cause vitamin D deficiency. Also, vitamin D is available in dietary supplements and foods such as salmon and eggs, as well as enriched milk and orange juice.

• If it's cold or cloudy outside, you don't need sunscreen.

This is not true. Up to 40 percent of the sun's ultraviolet radiation reaches the earth on a completely cloudy day. This misperception often leads to the most serious sunburns, because people spend all day outdoors with no protection from the sun.

• Eighty percent of your sun exposure comes as a child, so it's too late to do anything now.

It appears that this universally promoted idea was based largely on a misinterpretation. A recent multi-center study showed that we get less than 25 percent of our total sun exposure by age 18. In fact, it is men over the age of 40 who spend the most time outdoors, and get the highest annual doses of UV rays. And since adult Americans are living longer and spending more leisure time outdoors, preventing ongoing skin damage will continue to be an important part of a healthy lifestyle.