Sunscreen is one of the healthiest things you can use to protect your skin from the sun. A good sunscreen with potent UVA and UVB blocking agents can keep you from getting burned, minimize the development of wrinkles and other signs of aging, and can reduce your risk of skin cancer, according to the U.S. Food and Drug Administration (FDA). That last part is important, because more than five million new cases of nonmelanoma skin cancer (basal cell carcinoma and squamous cell carcinoma) are diagnosed in the United States each year, according to the Skin Cancer Foundation.

The American Academy of Dermatology (AAD) recommends sunscreen that’s broad-spectrum and water-resistant, with an SPF of 30 or higher. The board-certified dermatologist Sandy Skotnicki, MD, the founding director of Bay Dermatology Center in Toronto and an assistant professor at the University of Toronto, recommends choosing a mineral sunscreen with zinc and titanium for everyday use. Mineral sunscreens, which are also known as physical sunscreens, shield the skin from the sun’s rays and tend to be less irritating and more moisturizing than chemical sunscreens, which work by absorbing the rays and converting them to heat in the body, according to Piedmont Healthcare.

Your job’s not done when you choose the perfect bottle, though. Too many people manage to mess up the application process — dotting on too little, skipping vulnerable spots, and more. The most serious result of forgoing sunscreen is skin cancer, but that’s not the only reason to apply it. According to the Cleveland Clinic, sunburns damage the skin cells and blood vessels and can cause skin to look older, more wrinkled, dry, discolored, and leathery.

Dr. Skotnicki says the aging effect of the sun’s rays is a key reason to be diligent about sunscreen application. “There are several large studies to show regular sunscreen use can decrease photoaging over time — redness, brown spots, and wrinkles,” she says. In one study, for example, researchers found UV exposure to be responsible for about 80 percent of visible signs of aging on the face. A review in the American Journal of Clinical Dermatology published in August 2021 noted there is good evidence that daily sunscreen can prevent photoaging. What’s more, sunscreen may reverse the signs of aging too when antioxidants and photolyses (enzymes that repair DNA damage) are added.

Here, dermatologists share the biggest sunscreen slipups we tend to make, and how to avoid them.

1. You Wait Until You’re Already at the Beach to Apply Sunscreen

If you’re ankle-deep in sand when you slather on sunscreen, expect to come home looking like a lobster. Apply sunscreen at least 20 minutes before you step outdoors, because it takes that long for your skin to absorb the protective ingredients, says Leslie Baumann, MD, a dermatologist in Miami. Smooth it on as evenly as possible before getting dressed to avoid missing spots.

2. You’re Too Stingy When Applying Your Sunscreen

To get the advertised SPF, a little dab won’t do. “Most people apply too little, which can leave streaks and results in a lower SPF,” Skotnicki says. On beach days, coat your body fully with at least 1 ounce (a shot glass full) of sunscreen, per the AAD. If you aren’t sure what that looks like, there are hacks you can turn to. One option is Sunshotz ($8.49, Sunshotz.com), which is a portable measuring cup for sunscreen. (Everyday Health’s medical reviewer Ross Radusky, MD, a board-certified dermatologist, designed the product.) As for your face, the Skin Cancer Foundation suggests a nickel-size amount for this part of your body.

3. You Miss Important Areas

You must apply sunscreen to all areas that’ll be exposed to the sun, and there are a few spots people tend to miss. A study published in April 2019 in the journal PLoS One found that nearly 20 percent of participants did not apply sunscreen to their eyelids, and the study participants had no idea they’d missed this spot. That’s worrisome, because the skin on the eyelid has the highest incidence of skin cancer per unit area.

Lips are another often-missed area, and they're susceptible to damage because they don’t have much melanin, which is the protective pigment responsible for giving the skin, hair, and eyes their color. The Skin Cancer Foundation recommends wearing a lip balm or lipstick with SPF 15 or higher and paying particular attention to the bottom lip. Wearing lip gloss without any coverage is a big no-no, says Doris Day, MD, a clinical associate professor of dermatology at the New York University Langone Medical Center in New York City. “The more hydrated your lips are, the easier it is for UV rays to penetrate deeper into unprotected skin,” she says. As with baby oil on the rest of your skin, shiny, moist lips attract the sun, according to the Skin Cancer Foundation.

4. You Don’t Bother to Reapply Your Sunscreen

A survey published in May 2021 by the AAD found that only about 33 percent of Americans reapply their sunscreen as often as recommended, which means they're leaving skin protection on the table. “It’s not a magic potion that protects you forever,” says Andrew Kaufman, MD, the medical director of the Center for Dermatology Care in Thousand Oaks, California, and a clinical associate professor of medicine at UCLA School of Medicine in Los Angeles. The golden rule: Reapply sunscreen at least every two hours, more often if you perspire heavily or go swimming.

Per FDA guidelines, even sunscreens labeled “water resistant” maintain their SPF only for up to 80 minutes. (The label on water-resistant sunscreens will say whether it stays effective for 40 minutes or 80 minutes in water.) Reapplying will also help you achieve more even overall coverage, Skotnicki says.

5. You Don’t Spread Your Sunscreen Smoothly Enough

If you don’t apply the sunscreen evenly, you won’t tap into the protection promised on the label. Pay close attention as you’re applying, and go over the exposed areas multiple times to maximize coverage. Spray sunscreens that don’t require any rubbing can help alleviate this problem — just be thorough when applying. Sprays are convenient, but it can be hard to know if you’ve covered all exposed areas. Continue spraying until your skin glistens and then rub it in to ensure you’re fully covered.

6. You Skip Sunscreen When It’s Cloudy

Even when the sun is nowhere to be seen, 80 percent of its UV rays still hit your skin. Yet only about 20 percent of Americans apply sunscreen when it’s cloudy. Windows block UVB rays, but most let UVA rays through, so it’s important to apply sunscreen anytime you go outside — regardless of cloud coverage.

“People have a misconception about how much sun they get. They don’t realize that you don’t have to lie on the beach to soak up the sun,” Dr. Kaufman says. He advises placing your sunscreen right next to your toothpaste as a reminder to apply it every day.

7. You Ignore the Expiration Date

Have you been using the same bottle of sunscreen year after year? You may be putting your skin at risk. The FDA requires sunscreen to last at least three years. After that, it may not provide the amount of protection listed on the bottle. Consult the expiration date before applying, and if you don’t see one, assume it expires three years from the date of purchase. Note the purchase date on the bottle so you can keep track.

Additional reporting by Karyn Repinski.