Like brushing, flossing, and eating vegetables, it’s important to wear sunscreen—whether we like it or not. When you let your sun safety habits slide, you leave your skin vulnerable, not only to sun damage that will cause wrinkles and brown spots but also possibly to life-threatening cancer. An estimated one in five Americans will develop some type of skin cancer in their lifetime, according to the American Academy of Dermatology (AAD).

And although genetics can certainly affect your skin cancer risk, proper use of sun protection plays a huge role in prevention. In fact, a study published in 2010 in the Journal of Clinical Oncology found that daily sunscreen use may cut the risk of melanoma (the deadliest form of skin cancer) in half.

The key, however, is not just to wear sunscreen but to wear it properly. And research shows that many people don’t. For example, a new study published in the Journal of the American Academy of Dermatology examined sunscreen use in more than 2,000 state fair attendees. Free sunscreen dispensers were placed at 10 fair information booths. Only 33 percent of people who used them applied sunscreen to all of their exposed skin. The rest focused only their faces and arms—leaving plenty of other areas unprotected.

“People were most likely to ignore their legs,” says Ingrid Polcari, M.D., assistant professor of dermatology at the University of Minnesota Medical School and one of the study authors. “For too many people, sun protection is not a priority. They either underestimate the risks of the sun or find sunscreen a hassle or too messy."

How savvy a sunscreen user are you? We’ve listed eight common sun-protection beliefs below. Take a look and see if you can separate the myths from the facts.

Myth or Fact? If I Put Sunscreen on in the Morning, I’m Covered All Day.

MYTH: Unlike some deodorants or allergy medications that promise 24-hour protection, there is no such thing as a long-lasting sunscreen. “Once it’s on the skin, sunscreen begins to chemically wear down, and after a couple of hours it becomes less effective,” says David J. Leffell, M.D., professor of dermatology at the Yale School of Medicine. The AAD recommends reapplying every 2 hours or immediately after swimming or heavy sweating.

Myth or Fact? An 8-Ounce Tube of Sunscreen Shouldn't Last Through Your Weeklong Beach Vacation.

FACT: When you’re at the beach or pool—and the majority of your skin is exposed in a bathing suit—guidelines call for using a full ounce of sunscreen (a blob about the size of a golf ball) per application. And given that you’re supposed to reapply every 2 hours or immediately after swimming, you should go through several ounces during a single day spent outdoors. “When a patient tells me they’ve had the same bottle all summer, I know they’re not using enough or reapplying as they should,” says Joel L. Cohen, M.D., Director of AboutSkin Dermatology in Denver and a member of the teaching faculty at the University of Colorado and the University of California at Irvine. For a nonbeach day, when only your face and arms are exposed, you still need to use a teaspoon-sized dollop of sunscreen for your face, neck, and ears, and another one for each arm.

Myth or Fact? I Don’t Need Sunscreen on Cloudy Days.

MYTH: Seeing clouds in the sky can give you a false sense of security, but the truth is that the sun’s UV rays still reach your skin you even when it’s overcast. In the state fair study, the number of people who used sunscreen on overcast days was about half, on average, vs. sunny days. “It’s a common misconception that clouds will prevent sunburn,” Polcari says, “but up to 80 percent of UV rays can penetrate the clouds and damage skin.”  

Myth or Fact? A Sunscreen With a High SPF Won’t Protect My Skin Longer.

FACT: “The higher numbers, in general, are marketing,” Leffell says. An SPF 100 doesn’t give you double the protection of an SPF 50—or last twice as long, In fact, when applied correctly, SPF 50 blocks about 98 percent of UV rays, and SPF 100 blocks only 1 percentage point more. And regardless of the SPF number, all sunscreens lose effectiveness over time. "It's absolutely true that you need to apply as much and as often,” Leffell says.

Myth or Fact? I Need a Hat Even If I’m Using Sunscreen.

FACT: Even the best sunscreen applied properly can’t give you 100 percent protection from UV rays. And let’s face it, few of us are as diligent with sunscreen as we need to be. Doubling up on protection—by wearing sunscreen plus sun-protective clothing and a wide-brimmed hat—will help ensure that you’re as safe as possible in the sun.  

Myth or Fact? Skin Cancer Doesn’t Run in My Family, so I Don’t Have to Worry Too Much About Sun Protection.

MYTH: A genetic predisposition to skin cancer is just one piece of the puzzle, and one you can’t really control. But you can control how much sun exposure you get. Regardless of whether skin cancer runs in your family, protecting your skin is essential. The AAD estimates that avoiding exposure to UV rays could prevent more than 3 million cases of skin cancer every year. Because total avoidance of the sun isn’t really possible, using sunscreen properly and covering up are the next best ways to reduce your risk of skin cancer.  

Myth or Fact? I Need Sunscreen During All Daylight Hours.

FACT: The UV rays that cause sunburn (UVB) are strongest from 10 a.m. to 4 p.m. And although it’s not as likely that you’ll get sunburned if you’re outdoors sans sunscreen at 7 a.m. or 5 p.m. in the summer, you are still being exposed to UVA rays, which trigger the kind of damage to skin cells that can lead to sagging, wrinkling, and skin cancer. UVA rays are present year-round as long as the sun is up, even on cloudy days.  

Myth or Fact? If I Didn’t Wear Sunscreen as a Kid, Starting Now Won’t Help Protect Against Skin Cancer.

MYTH: For years, experts wrongly believed that people got most of their sun exposure before age 18. Here’s the reality: By age 40, you’ve racked up only half of your lifetime dose of UV rays; by age 59, just 74 percent. And for those older than 50, being in the sun sans protection can be particularly dangerous. Your body begins to lose its ability to repair the cell damage created by the sun’s rays, and your immune system weakens, making you more susceptible to skin cancer. Bottom line: You’re never too old to use sunscreen.