As a long-time beauty editor who practices what she preaches, I slather sunscreen on my face every. single. day. I’ve been doing that for decades, rain or shine, and it’s a point of pride for me—but I have had plenty of SPF embarrassments too, and by that I mean sunburns. Like the time when my cross-body bag rubbed off all the sunscreen on my shoulder and left me with a scarlet diagonal line, or the spots I somehow missed for no reason (like a swath of my upper left arm last weekend) that left my skin on fire.

Turns out I’m not alone. SPF mistakes happen, but the biggest mistake is not applying sunscreen at all. “Consistency matters more than perfection,” says Cheryl Karcher, M.D., a board-certified dermatologist at Center Aesthetic & Dermatology in New York City. “Daily sunscreen use is one of the simplest and most effective ways to prevent premature aging, hyperpigmentation, and skin cancer,” she says.

I went straight to two expert dermatologists to get the scoop on all the ways you’re (probably) applying your SPF wrong. Practically everyone has made one of the most common sunscreen mistakes on this list.

“Most people do not apply enough sunscreen, with people often applying only about 25 to 50% of the amount needed to achieve the SPF listed on the label,” says Marisa Garshick, M.D., FAAD, a board-certified dermatologist at MDCS Dermatology in New Jersey. “For the body, the general recommendation is about one ounce, roughly a shot glass full, per application, and for the face and neck, about a nickel-sized amount or the equivalent of two finger lengths.”

Sunscreen should be reapplied every two hours, and more often if you’re swimming or sweating. “People forget constantly, so I recommend setting a phone alarm or reapplying at routine moments like after lunch or after getting out of the water,” Dr. Karcher says.

To make reapplication a cinch, Dr. Garshick suggests keeping a sunscreen stick or powder in your bag for touch-ups to make it easy and convenient for on-the-go.

“UV rays can still penetrate through clouds, meaning sun damage can occur even on cloudy or rainy days,” Dr. Garshick says. “This is why daily sunscreen use is important, regardless of season or weather, because UV exposure can be cumulative over time.”

Dr. Karcher cautions that up to 80 percent of UV rays can still penetrate clouds. “Many people get some of their worst sunburns when they underestimate cloudy weather,” she says.

Sun safety requires a teensy bit of planning. “Applying sunscreen before you go outside ensures that you are properly protected even with initial exposure,” Dr. Garshick says. “In general, I recommend applying sunscreen about 15 minutes before sun exposure, especially with chemical formulations, to allow the product time to settle.”

Yep, this one gets me way more often than I’d like to admit. “The ears, eyelids, lips, scalp, neck, tops of the feet, and backs of the hands are very commonly missed,” Dr. Karcher says. “These are also areas where we frequently diagnose skin cancers and precancers.” Let’s not forget the signs of premature aging, either—no one wants old-looking hands.

Think of a foundation with SPF as bonus sun protection—not the main source. “While makeup containing SPF can offer some added protection, most people do not apply enough makeup to achieve the SPF level listed on the packaging,” Dr. Garshick says. “It is best to use a dedicated broad-spectrum sunscreen underneath makeup rather than relying on makeup alone for sun protection.

Throwing out SPF in this economy? Yes, times are tough, but that’s a must if your SPF has passed its sell-by date. Permanently damaging your skin isn’t worth saving a few bucks. “Expired sunscreen may lose stability and effectiveness over time, meaning you may not be getting the UV protection listed on the bottle,” Dr. Karcher says. “Heat exposure, like leaving sunscreen in a hot car or beach bag, can also degrade active ingredients faster.”

In some cases, expired sunscreen can also change in texture, smell, or consistency, and may cause skin sensitivity or irritation, Dr. Garshick warns.

Sometimes numbers really do count, and this is one of them. “Using a sunscreen with too low an SPF level may not provide adequate protection, especially if someone is outdoors for prolonged periods or not applying enough product,” Dr. Garshick says. “I generally recommend choosing a broad-spectrum sunscreen with at least SPF 30, as SPF 30 blocks about 97 percent of UVB rays. Higher SPFs can provide additional protection, particularly for individuals with photosensitive conditions or a history of skin cancer, but it is important to still apply enough and to reapply to get the SPF amount listed on the label.”

Regular sunscreen is fine for most days, but using a water-resistant formula on sweaty days or while you’re swimming is crucial. “Regular sunscreen can break down or wash off quickly with sweat and water exposure,” Dr. Karcher says. “Water-resistant formulas adhere better to the skin and help maintain more consistent protection during outdoor activities.” However, remember that water-resistant sunscreens still need to be reapplied according to the instructions, typically every 40 or 80 minutes, depending on the formula.

Hats and UPF clothing can be your besties. And chic options really do exist. “Sunscreen is just one part of a complete sun protection strategy,” Dr. Garshick says. “No sunscreen blocks 100 percent of UV rays, even with perfect application, and factors like missed spots or inadequate application can reduce protection. Incorporating protective clothing, wide-brimmed hats, sunglasses, and seeking shade, especially during peak UV hours, provides an additional layer of protection from UV damage.”

We’ll say it again: Wearing sunscreen is a must every single day, regardless of the season or weather. “Another common mistake is applying sunscreen only when going to the beach or pool instead of making it part of a daily routine,” Dr. Garshick says. “The best sunscreen is the one you will use, so find a sunscreen you like to wear and stick with it because consistency is key when it comes to sun protection.”

Even incidental sun exposure can take a toll on skin. “People often forget to use sunscreen daily, even during short periods of incidental sun exposure like driving or walking the dog,” Dr. Karcher says.

Everyone needs sunscreen, regardless of the color of their skin. “Another major mistake is assuming darker skin tones do not need sunscreen, when UV damage and skin cancer can still absolutely occur,” Dr. Karcher says.

Dr. Garshick points out that many formulations are great for all skin tones, including those with darker skin.

“People with acne worry that sunscreen will make them break out more, so they choose not to wear it,” Dr. Garshick says. “Instead, it is important to find a sunscreen formulation that is non-comedogenic and won't clog the pores and may actually help improve the appearance of blemishes. Everyone, regardless of skin type or tone, can experience sun damage and should wear sunscreen regularly.” EltaMD UV Clear Blemish-Prone and Oil-Balancing Sunscreen is a great pick for acne-prone skin.

• Cheryl Karcher, M.D., is a board-certified dermatologist at Center Aesthetic & Dermatology in New York City.
• Marisa Garshick, M.D., FAAD, is a board-certified dermatologist at MDCS Dermatology in New Jersey.

Celia Shatzman (she/her) is a Brooklyn-based journalist who has covered beauty for two decades and considers daily SPF her anti-aging secret.