Photo: Sabine Villard/Trunk Archive

Choosing the Right Formula
Sunscreens come in two forms: Physical sunscreens, such as zinc oxide and titanium dioxide, are minerals that sit on the skin's surface and reflect the sun's rays like tiny mirrors. Chemical sunscreens, such as avobenzone and oxybenzone, work like little sponges to absorb and neutralize solar energy. Physical blockers can deflect both types of rays: UVA and UVB. Chemical ingredients may defend against only one or the other. Look for broad spectrum on the label to make sure the product you use covers both.

There are pros and cons with each form. While physical blockers very rarely cause an allergic reaction, a small percentage of the population is allergic to avobenzone or oxybenzone, according to Darrell Rigel, MD, clinical professor of dermatology at New York University Langone Medical Center. "The main problem with physical sunscreens is that they tend to be less water-resistant," Rigel says. "You put them on and go in the pool or sweat, and they can just run off." If you're the sporty type, select a chemical sunscreen, which is more likely formulated to resist water and perspiration. No matter what kind you end up choosing, "you need at least an SPF 30 every day," says Rigel.

Making Sure Your Sunscreen Works
If dermatologists could tell you one thing about the way you apply sunscreen, it's this: You're skimping. To shield your face and body adequately when you're outdoors, experts say you need a full ounce of sunscreen (equivalent to a shot glass). And you need to reapply that amount every two hours—more often if you're getting wet. (Water-resistant sunscreens are rated for 40 or 80 minutes—check the label. After that, it's time for another coat.) So even if you're spending only a long weekend in Bermuda, a couple of TSA-approved bottles won't cut it. When your day is spent mostly indoors, it's okay to say "one (coat) and done." "You still need an SPF 30, but you can put it on in the morning and not reapply unless you go out for errands," says Rigel.

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Stop! Now Read This
If you've got skin, the following applies to you.

There are two types of skin cancer. Nonmelanoma—basal cell or squamous cell carcinoma—usually looks like a little pimple or sore, may also bleed and doesn't go away after a few weeks. "Anything that's bleeding, scabbing, crusting and not healing needs to be checked by a dermatologist," says Lisa Chipps, MD, assistant clinical professor of dermatology at Harbor-UCLA Medical Center. Melanoma is a potentially deadly form that often shows up as an irregular mole. Follow the ABCDE guide. If your spot fits any of the descriptions below, get yourself to a dermatologist, stat.

Asymmetry: one side is different from the other
Borders: scalloped or irregular edges
Color: multiple shades instead of a uniform brown hue
Diameter: larger than a pencil eraser
Evolving: anything that changes in size, shape or color over time

Special Alert
Attention, darker-skinned women: You are more susceptible to a specific form of melanoma that tends to develop on palms and soles, says Carlos Charles, MD, clinical instructor of dermatology at Weill Cornell Medical College. It may also appear as a linear pigmented band on the nail bed, so check those areas regularly.

Illustration: Gillian MacLeod

Photo: Marko Metzinger

The Best Defense
Don't leave the house this summer without one of these ten hardworking bodyguards.

1. Clarins UV Plus Anti-Pollution Broad Spectrum SPF 50, $42;
2. SkinMedica Total Defense + Repair SPF 50, $75;
3. Shiseido Ultimate Sun Protection Cream SPF 50+, $36;
4. Paula's Choice Resist Anti-Aging Lip Gloss SPF 40, $18;
5. SkinCeuticals Physical Matte UV Defense SPF 50, $34;
6. L'Oréal Paris Advanced Suncare Invisible Protect Clear Finish Spray SPF 50, $11; drugstores
7. La Roche-Posay Anthelios 60 Cooling Water-Lotion Sunscreen SPF 60, $36; drugstores
8. Coppertone Ultra Guard AccuSpray Sunscreen SPF 30, $10; drugstores
9. Avène Ultra-Light Hydrating Sunscreen Lotion SPF 50+, $24; drugstores
10. Neutrogena CoolDry Sport Sunscreen Lotion SPF 30, $10.50; drugstores

Photo: Ridofranz/iStock/Thinkstock

Inquiring Minds Want to Know...
What's the best sunscreen?
"The one you'll wear every day—as long as it's broad spectrum and at least SPF 30," says Chipps. "You have to like the texture, or you aren't going to use it. It's a personal preference, and finding yours may take some trial and error."

Won't sunscreen make my oily skin break out?
It's not the sunscreen agents causing your pimples; it's the formula, says Rigel. If blocked pores are a problem, look for OIL-FREE or NONCOMEDOGENIC on the label.

Is the SPF in my makeup enough?
That would be a resounding no, say dermatologists. "If you wear a thick coat of foundation all over your face, then maybe," says Chipps. "But most people don't—they apply a thin layer and put on only a little extra if they're covering a blemish." If you want to thwart the rays, first smooth on a lightweight sunscreen, then put on your makeup.