The ABCs Of SPF: Everything You Need To Know About Sunscreen

Welcome to SPF 101. Learn how sunscreen works, so you can avoid getting burned this summer.

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You’ve probably heard a million times that wearing sunscreen is critical for your skin’s health—and ideally, you sport SPF on the daily, even when it’s not sunny out. (The sun can still damage your skin when it’s cloudy, FYI.) Even if that’s not quite the case, with summer quickly approaching, we get that you might be thinking a whole lot more about sunscreen now than you did in the dead of winter. But how much do you actually know about what SPF is and how it works? Understanding SPF will go a long way in using it properly to protect your skin from the sun’s damaging UV rays.

What does SPF actually mean?

SPF stands for Sun Protection Factor, and it’s a measure of how long a sunscreen will protect you from UVB rays, says Fayne Frey, MD, a board-certified dermatologist in West Nyack, New York. The number next to SPF (e.g. 15 or 30) tells you how much time it’d take for your skin to turn red while wearing SPF compared to how long it’d take your skin to turn red without wearing SPF. For example, if it would take 20 minutes for your skin to burn without sunscreen, using an SPF 15 sunscreen would prevent burning for 15 times longer, which is about 5 hours, according to the Skin Cancer Foundation. That doesn’t mean SPF 100 offers a ton more protection than SPF 15 or 30 though. The Skin Cancer Foundation also notes that SPF 15 blocks about 93 percent of UVB rays, SPF 30 blocks about 97 percent of UVB rays, and SPF 50 blocks about 98 percent of UVB rays. And even if you’re using a high SPF, it’s not going to do much for you unless you remember to reapply it regularly. Keep reading to find expert tips on applying sunscreen efficiently.

Is SPF all you have to look for on a sunscreen label?

Nope. To shield your skin against both UVA and UVB rays, you have to look for the phrase “broad-spectrum” on sunscreen labels, says Tsippora Shainhouse, MD, a board-certified dermatologist in Los Angeles and clinical instructor at the University of Southern California. The sun emits three types of rays: UVA, UVB, and UVC. “UVA rays have the longest wavelengths, UVB rays have shorter wavelengths, and UVC rays are even shorter,” says Frey. “UVC rays don’t reach Earth’s surface, so you don’t have to worry about them.” Because of their longer wavelengths, UVA rays have the ability to penetrate deeper into your skin than UVB rays, and they are the ones that can contribute to the formation of wrinkles and hyperpigmentation that show up years later, says Frey. “UVA rays were never really thought to cause burns and cancer, but recently we’ve learned that that’s not the case,” says Frey. “Research shows that UVA rays do cause skin cancer.” UVB rays, which damage the top layer of your skin, are responsible for sunburns as well as skin cancer. (An easy way to remember what’s what? Think A for accelerated aging and B for burns, says beauty industry chemist David Pollock.)

The ABCs Of SPF: Everything You Need To Know About Sunscreen
In 2011, the Food and Drug Administration (FDA) updated its guidelines for how sunscreens are sold in the U.S. Manufacturers now have to pass a specific test if they want to label a sunscreen broad-spectrum in an effort to ensure that what you buy will actually protect you from UVA and UVB rays. Additionally, sunscreen labels can no longer say waterproof on them, says Shainhouse. “Instead, the label will read ‘water-resistant,’ which means that it will last up to 80 minutes in water or with profuse sweating,” says Shainhouse. And, fun fact: Brands can no longer call their products sunblock, either. “There is no such word as sunblock anymore because you cannot completely block the UV rays with a topical cream,” says Shainhouse. Hence the term sunscreen.

What happens when you skip SPF?

We get it: Sometimes life happens, and you just don’t have the time to apply sunscreen. But if you’re thinking this is an unnecessary step in your daily skincare routine, you might want to change your tune. Beyond shielding yourself from sunburns, broad-spectrum sunscreen helps protect you from premature aging caused by UVA rays. “Sunscreen should be applied on your face and hands every day,” says Frey. “You get more sun just going about your day—walking to your car and mailbox—than you do on those few days you spend on the beach. Sun damage accumulates.” Even sitting by a window or being stuck in traffic could leave you vulnerable. “UVA rays penetrate through glass,” says Frey, “so even when you’re driving, you get exposure.” If you were to compare the face, hands, and neck of a middle-aged person to their butt, well, the commonly exposed areas would likely look a whole lot older if sun protection wasn’t a priority, says Frey. Sure, you don’t need to wear SPF under your clothes in January, but “it’s truly necessary for people to apply sunscreen [to exposed areas] every day of the year,” says Frey. According to a 2014 study published in the journal Molecules, it’s possible that UV exposure in general accounts for as much as 80 percent of visible aging signs, like lines, dryness, and hyperpigmentation—and that this photoaging is associated with an increased risk for skin cancer. Per the American Cancer Society, skin cancer is the most common type of cancer. Basal and squamous cell carcinomas (the two most-diagnosed forms of skin cancer) are typically found on areas that are exposed to the sun, like your head, neck, and arms. Basal and squamous cell carcinoma are easily treatable if caught early, but melanoma, which is less common, is harder to treat because it grows and spreads quickly. Research has found that using sunscreen with an SPF 15 or higher curbs your risk of squamous cell carcinoma by 40 percent and your risk of melanoma by 50 percent, says Shainhouse.

What’s the best SPF formula?

SPF isn’t one size fits all, and now that you know why it’s crucial to apply SPF, it’s time to find the formula that best suits you. There are actually two types of sunscreen: chemical and physical. Chemical ingredients like avobenzone absorb UV rays and keep them from penetrating your skin, says Frey. Physical (or mineral) sunscreen contains ingredients like titanium dioxide or zinc oxide that sit on top of your skin and deflect UV rays, says Shainhouse. There are pros and cons to both, though. Chemical sunscreens typically have more cosmetically elegant formulas (meaning they don’t leave a white film and won’t mess with your makeup, says Frey). Shainhouse adds that chemical sunscreens are also more likely to have accurate SPF levels. Still, some ingredients in chemical sunscreens, like oxybenzone, can be highly irritating, especially if you’re prone to sensitivity, says Pollock. Overall, Pollock prefers a physical sunscreen that’s formulated with a combo of titanium dioxide and zinc oxide for sun protection with the least amount of irritation. Pollock notes that if you’re looking for a more natural, potentially safer SPF option, then you’re going to want to use a physical sunscreen. It may leave a white cast on your skin, says Frey, but with newer formulations, this is becoming less of a problem. It’s important to note that physical sunscreen rubs off more easily, so it may need to be reapplied more frequently, says Shainhouse. Because of the possibility for irritation, physical sunscreen is also the best option for babies, says Frey. However, she points out that “baby sunscreen” is almost completely a marketing ploy. Almost all baby and kid sunscreens have physical formulas, and they often have the same exact formulas as other sunscreens, just with a different label on the front. The only thing that might be different about baby sunscreen is that it’d probably be fragrance-free, says Pollock, since fragrance is an irritant. “At the end of the day, the FDA only looks at actives [in sunscreen],” says Pollock. “The government doesn’t care if it’s for a baby or a 90-year-old. They only care about whether it blocks the sun.” Finally, keep the environment in mind. A 2008 study published in the journal Environmental Health Perspectives found that chemical sunscreens can cause coral reef damage. The researchers found that at least 25 percent of sunscreen is washed off while swimming within 20 minutes. The National Park Service advises using physical sunscreen, since titanium dioxide and zinc oxide haven’t been found to damage reefs.

What’s the best form of sunscreen?

Once you choose between chemical and physical SPF, you then have to decide which form of sunscreen to wear. You have a lot of options, from lotions to sprays to sticks. Lotions give you better control because you can see exactly how much you’re applying, says Pollock, while sprays are super convenient and a great pick for the laziest among us, he says. Personally, Pollock is a fan of stick sunscreen for the forehead and around the eyes. That’s because if you’re using a chemical SPF lotion on your face, and you sweat, it could run into your eyes and cause burning, whereas a stick won’t run.   Experts say they’re all relatively effective—as long as you apply and reapply—so it’s more about personal preference. The only caveat is when it comes to makeup with SPF. “It’s better than nothing, but the truth is most people don’t put makeup on thick enough,” says Frey. “It’s best to put sunscreen on first.”

What’s the best way to apply sunscreen?

“The most important thing isn’t what number you use, it’s how you use it,” says Frey. “Even if you use SPF 100, you’re not going to get the SPF 100 protection unless you do it correctly.” Chemical SPF takes about 15 minutes to absorb, so you have to apply it before you go outside according to the American Academy of Dermatology. Experts recommend using at least one ounce (which is about the size of a shot glass) to cover exposed areas. One ounce is usually sufficient to cover exposed skin in an adult from head to toe,” says Shainhouse. “I usually recommend a nickel-sized dollop for face and ears or a quarter-sized if you’re including your entire neckfront, sides, and back.” This is all dependent on body size, says Frey—someone larger would need to apply more. (Commonly overlooked areas include the tops of the feet, scalp, ears, and around bathing suit edges, says Frey, so don’t forget about protecting those places, too!) If you’re using an SPF lotion, gel, or oil, rub it in thoroughly for maximum benefits. If you’re using a  spray SPF sunscreen, you also have to rub that in, but you should apply a second layer to make sure you’re not missing any spots, says Shainhouse. “Spray sunscreens are only effective if applied properly, which means holding the bottle two to three inches from the skin and spraying a stream onto the skin,” she says. Just don’t spray SPF directly onto your face, since it can get into your lungs and irritate them, says Frey. If you are planning to use spray sunscreen on your face, spray it into your hands first and pat it onto your face. As far as reapplication goes, experts recommend doing so approximately every two hours. Because the UVA protection begins to break down after two hours, sunscreen should be reapplied every two to three hours if you are out in the sun,” says Shainhouse. “They should be reapplied more frequently if you sweat profusely or go swimming.” There are other sun protection measures you should take besides applying sunscreen, the biggest being avoiding midday sun exposure, says Frey, since the sun is at its peak between 10 a.m. and 2 p.m. Other than that, throw on a hat to shield your scalp and sunglasses to protect your eyes. UPF clothing is an effective way to protect your skin, too. “Some of the fabrics are fantastic,” says Frey. When it comes to clothing in general, Frey says that darker tops are better because the sun can get through white t-shirts.

How do you pick the best SPF?

As with any other skincare product, keep your skin type and lifestyle in mind when choosing an SPF sunscreen. SPF for acne-prone skin: Look for a non-comedogenic, oil-free formula, like Neutrogena Clear Face Sunscreen Lotion ($12), which is formulated with chemical SPF and won’t clog pores or cause breakouts. SPF for oily skin: EltaMD UV Clear Broad-Spectrum SPF 46 ($33) is formulated with lactic acid, which unclogs pores and curbs shine, making it a perfect chemical SPF pick for oily skin. SPF for dry skin: Hydrate dry skin with a moisturizer with SPF like Paula’s Choice Resist Skin Restoring Moisturizer with SPF 50 ($33), which contains nourishing shea butter and has a chemical SPF formulation. SPF for sensitive skin: Choose a physical sunscreen, like Avene Mineral Ultra-Light Hydrating Sunscreen Lotion SPF 50+ ($28), which features the brand’s soothing spring water. SPF with anti-aging benefits: Packed with antioxidants, Drunk Elephant Umbra Sheer Physical Daily Defense Broad Spectrum Sunscreen SPF 30 ($34) is a mineral SPF sunscreen that protects against free radical damage that can cause wrinkles.   SPF for makeup prep: Avoid your foundation slicking by applying Supergoop Unseen Sunscreen Broad Spectrum Sunscreen SPF 40 ($32) before makeup. It has an oil-controlling formula that leaves skin with a velvety finish. SPF for lips and ears: Reach for an easy-to-apply stick SPF sunscreen, like Bare Republic Mineral Sport Sunscreen Stick SPF 50 ($10), to cover these often-forgotten areas. SPF for body: La Roche Posay Anthelios Face & Body Melt-In Sunscreen Milk SPF 60 ($36) is a classic for a reason. It has a non-greasy, oil-free formula that absorbs easily into skin without clogging pores. SPF for beach trips: Spray your arms and legs with reef-safe All Good Sport Sunscreen Spray SPF 30 ($17), and relax while staring out into the ocean. SPF for on-the-go touch-ups: When you’re in need of a quick SPF touch-up, that’s the time to reach for a powder sunscreen, like Colorescience Sunforgettable Total Protection Brush-On Shield SPF 50 ($65), which provides mineral protection and won’t mess with makeup. Regardless of which sunscreen you use, know that SPF has about a three-year shelf life, says Frey. That being said, because you should wear sunscreen on exposed areas every day, your bottle or tube of SPF shouldn’t come close to lasting for three years.

Christina Heiser
Christina Heiser is a beauty, health, and wellness writer with more than eight years experience working in digital media. In addition to contributing to HealthyWay, she also currently writes for NBC News, Total Beauty, The Pretty Pimple, A Sweat Life, and Vitamin Shoppe. When she's not working, you can find Christina hitting up boutique fitness classes in New York City, cheering on her favorite sports teams (Let's go, Mets!), and watching as many Broadway plays as she can fit into her schedule.