Test yourself on the subtle and surprising ways you could be vulnerable to skin cancer.

By Stacey Colino

Sun Protection 101

"Applying sunscreen in your 40s or 50s can make a big difference in decreasing the threat of skin cancer," says David J. Leffell, M.D., a professor of dermatology and surgery at the Yale School of Medicine and author of Total Skin. "Even if you have some damage to the skin, sunscreen will enable you to stop repeated injuries to those areas. And if you block UV radiation, some of the precancerous cells may regress or disappear." Here's how to do it right.

Choose the best sunscreen. Experts recommend using a broad-spectrum product with an SPF of at least 30 (such as the new Coppertone ClearlySheer formula or Neutrogena's Beach Defense line) to protect against UVA and UVB rays. You might also consider one that contains novel ingredients like green tea, vitamin C or pomegranate extract, all rich sources of antioxidants.

Apply liberally. Thirty minutes before going outside, cover any exposed skin with sunscreen and thoroughly rub it in. Re-apply every two hours and after toweling off at the beach or pool.

Seek shade. "Early morning or late afternoon are the best times to be active outdoors," Dr. Leffell says. Stay in the shade between 10 and 4, when the sun's rays are at their most intense.

Cover Up. Wear sun-protective clothing and a pretty wide-brimmed hat (you'll ratchet up your style quotient too). Even if you sit under a beach umbrella, apply sunscreen, advises Albert Lefkovits, M.D., an associate clinical professor of dermatology at the Icahn School of Medicine at Mount Sinai in New York City. UV rays can reflect off the sand onto your face and body.

TRUE OR FALSE: Skin cancer always occurs on sun-exposed areas.

FALSE: It can develop even where the sun doesn't shine. While basal- and squamous-cell carcinomas typically appear on sun-exposed parts of the body, melanoma can occur on the buttocks, genitals, scalp and even between the toes and on the soles of your feet. "Melanoma can happen wherever there are pigment cells," Dr. Leffell explains. That's why it's important to see your dermatologist annually for a full-body examination and to inspect your skin regularly from head to toe for changes.

TRUE OR FALSE: The windows in your car, home and office protect your skin from UV rays.

FALSE: It's true that glass blocks most UVB rays, which are the primary cause of sunburn, but UVA rays, which penetrate the skin more deeply, can still get through. This means that even if you're inside your car or house, you're at risk for UV damage to your skin. You can have special window film installed that will block up to 99.9 percent of UV rays and/or you can protect your skin by wearing sunscreen even when you're driving or sitting by a sunny window in the comfort of your home.

TRUE OR FALSE: To spot a melanoma, the most dangerous form of skin cancer, you should be on the lookout for the ABCDEs: Asymmetry, irregular Borders, a variety of Colors, a Diameter larger than 1/4 inch on a lesion, and Evolution (or changes) over time.

TRUE: "But there are exceptions to almost every rule," Dr. Lefkovits says. If you notice a new pigmented lesion after age 40 or spot a fast-growing one on your skin, get it checked out by a dermatologist. Should any mole or other lesion bleed, itch or become crusty, these may be danger signs too, in which case you should get to a dermatologist—pronto.

TRUE OR FALSE: When you can't see your shadow, you can't get sunburned.

FALSE: You can get a sunburn and experience sun damage even on a cloudy day. Up to 80 percent of the sun's ultraviolet rays can penetrate through thin clouds and fog, according to the Skin Cancer Foundation. To gauge how much protection you'll need, check the UV Index in your area. And visit epa.gov/enviro/mobile to download the EPA's free SunWise UV Index app to your smartphone.

TRUE OR FALSE: Skin cancer is exclusive to the skin.

FALSE: It can affect your eyes as well as your lips—which are a different kind of skin. Squamous- cell cancer, and other cancerous growths, can develop on the lips. That's why it's essential to wear lip balm or lipstick with an SPF of at least 15 and reapply it regularly, or wear a physical UV blocker such as zinc oxide or titanium dioxide on your lips, Dr. Lefkovits says. By contrast, melanoma can occur inside the eye. If you have a family history of melanoma, schedule appointments with an ophthalmologist every year. To protect your eyes, wear sunglasses that block 99 percent of UVA and UVB rays and cover the entire eye area. This will help prevent cataracts too.

What Causes Skin Cancer?

Sun exposure is responsible for about 90 percent of all non-melanoma skin cancers. (Everything from genetics to overexposure to X-rays is to blame for the rest.) Being exposed to UV light triggers a domino effect, suppressing the immune system in the skin, leading to DNA damage of skin cells and inhibiting enzymes that repair injured cells, explains Lisa Donofrio, M.D., an associate clinical professor of dermatology at Yale University. Sunburn also sparks immune system changes that can lead to skin cancer.

Originally published in the June 2014 issue of Family Circle magazine.