Don't get burned: 5 ways you could be using sunscreen wrong

By now, everybody knows sunscreen is a crucial part of preventing skin cancer (and painful blisters and peeling!), even if dermatologists estimate only a third of us are using it.

But just squirting it on haphazardly isn't enough. Make sure you're using the right sunscreen the right way with these tips.

Lay it on thick — and keep putting it on

Don't rub and rub until the lotion disappears. You want your sunscreen to form a barrier in between your skin and the sun. In some cases, that might mean some white residue is visible. You want to use enough, too; the American Academy of Dermatology says to put on at least 1 ounce at a time, about enough to fill a shot glass. And keep reapplying at least every two hours, especially if you're swimming or sweating. If you're on an outdoor vacation or at the beach, a bottle shouldn't last you more than a day or two, so stock up.

Ix-nay the spray

Sure, aerosol sunscreen is convenient, but it could cost you in effectiveness. Studies indicate it's difficult to tell whether you're getting adequate coverage, since some of the sunscreen almost certainly floats away in the mist. You're not supposed to use it on your face, either — although you could spray it on your hands and apply it that way, it's just not as effective as using lotion or a sunscreen stick.

Know your numbers

For most people, SPF 30 is going to be adequate. Past studies suggest SPF 30 blocks about 97 percent of harmful rays; SPF 50 takes it up to about 98.5 percent. But a study published in this month's Journal of the American Academy of Dermatology found sunscreen with an SPF of 100 or higher is more effective than SPF 50 "during multiple periods of natural light exposure." This year, CVS stopped selling sunscreen below SPF 15 as part of its "Long Live Skin" campaign, which also includes educational materials in its stores. And also check the expiration date — sunscreen is only effective for about three years.

Broaden your protection

The sun emits two kinds of ultraviolet rays that can damage skin. UVB rays are the ones responsible for your painful sunburn. But UVA rays — which aren't blocked by cloud cover — are the ones that can cause cancers and age spots long-term. You want a sunscreen labeled "broad spectrum" to block both UVB and UVA rays, and use it even on cloudy days.

Don't forget your lips (and ears, nose, neck, face and scalp)

Any protruding feature is more susceptible to sunburn, and we're less likely to catch skin cancers early if they're in places we can't easily see. Lips, in particular, have less melanin, the pigmentation that provides some sun protection. But if you're dark all over, don't think that means you don't need sunscreen. Studies suggest dark-skinned people are more likely to get more aggressive skin cancers — perhaps in part because they're caught later. So spread on sunscreen now to avoid problems later.