What SPF do I need? How long does sunscreen last? What's the highest SPF? How does sunscreen work? The answers—plus the truth behind common sun protection myths, according to derms.

By Melanie Rud
Updated June 23, 2020
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By this point in life, you've (hopefully!) nailed your sunscreen M.O.…or have you? No need to go red in the face out of embarrassment (or from sun, for that matter). Step up your sun smarts with a little help from expert dermatologists.

Here, pros dispel common sun protection myths and answer some of your biggest SPF questions so you can ensure your skin is properly safeguarded throughout every season.

Myth: You only need to wear sunscreen when spending the day outside.

Repeat after me: Sun protection is non-negotiable 365 days a year, no matter where you are, what you're doing, or what the weather. "Most of the sun exposure people get is unintentional and incidental," says Joshua Zeichner, M.D., director of cosmetic and clinical research in dermatology at Mount Sinai Hospital in New York City. "People don't realize that it's during short moments spent outdoors—their commute to work, running errands—that the sun is damaging their skin."

That damage is cumulative; short bursts of time spent sans sunscreen have dangerous and long-lasting effects. And while burning UVB rays are stronger in the summer, UVA rays (which cause aging and skin cancer) are the same strength year-round and penetrate even on a cloudy day. Now, I know what you’re thinking: do I still need sunscreen if I’m spending the day inside? Yep—even if you’re quarantine. Luckily, the solution is simple. Make sunscreen a daily part of your routine, covering both your face and any other exposed areas, like your neck, chest, and hands—all common spots people forget to protect, according to Dr. Zeichner. (But what if you like to wear face makeup? Well, you could layer SPF under your foundation or opt for one of these best tinted face sunscreens.)

Myth: SPF 30 offers twice as much protection as SPF 15.

It might seem counterintuitive, but standard math principles don't apply when it comes to SPF numbers. "An SPF 15 blocks 94 percent of UVB rays, while an SPF 30 blocks 97 percent," explains Dr. Zeichner. The increase in protection once you go above an SPF 30 is only incremental, so in this case, the highest SPF sunscreen isn’t necessarily the best.

So, if you're sitting there asking yourself "what SPF do I need?" the short answer is SPF 30 for day-to-day use, according to Dr. Zeichner. (This is also the recommendation of the American Academy of Dermatology or AAD.) That said, it's not a bad idea to err higher and go with an SPF 50 when you're at the beach or pool, he says. "In order to get the level of protection labeled on the bottle, you need to both apply an adequate amount and reapply consistently, which most people don't do," he says. "By choosing a higher SPF, you're helping compensate for these discrepancies."

Now, the highest SPF sunscreen you'll see on store shelves is 100, but again, that's not going to give you twice the amount of protection as SPF 50. The increase from SPF 50 to SPF 100 offers a negligible difference of blocking 98 percent vs. 99 percent of UVB rays, respectively, according to the Environmental Working Group. Not to mention, these sky-high SPFs may make people think they can skimp on reapplication. "There can be a false sense of protection with an SPF of 100," Anna Chien, M.D., assistant professor of dermatology at Johns Hopkins School of Medicine, previously told Shape. These are all reasons why those SPF 100s may soon be a thing of the past; last year, the Food and Drug Administration (FDA) proposed that the maximum SPF label be capped at 60+. (Related: The FDA Is Aiming to Make Some Big Changes to Your Sunscreen.)

TL;DR— Your best bet is to use an SPF 30 daily, keep an SPF 50 on-hand for times when you're going to be in direct sun, and make sure to apply (and reapply) both as directed.

Myth: Dark skin can't get sunburned.

Ethnicities with darker skin aren't exempt from the daily sunscreen rule. “Skin pigment only offers the equivalent of an SPF 4," explains Dr. Zeichner. Aside from burning, there's also the universal risk of aging and skin cancer, since UVA rays affect skin equally—regardless of color. In fact, both the AAD and FDA uphold that everyone, regardless of age, gender, or race, can get skin cancer and, thus, can benefit from regular sunscreen use. The bottom line: All skin tones and types are susceptible to sun damage and need to be vigilant about protection.

Myth: You're safe if you sit in the shade.

Granted, sitting in the shade is a better option than sitting under direct sun, but it's not a substitute for sunscreen, cautions Dr. Zeichner. "UV rays reflect off the surfaces around you, especially when you're near a body of water." In other words, the rays are reaching you, even under an umbrella. In fact, a study published in JAMA Dermatology found that people sitting under a beach umbrella without sunscreen were more likely to burn than those in the sun who were wearing sunscreen. Rather than relying solely on shade, consider it only a part of your sun protection arsenal. "Seek shade, wear protective clothing, and, of course, be diligent about sunscreen application," advises Dr. Zeichner. (See also: Smart SPF Products That Aren’t Sunscreen)

Myth: It's better to use a cream sunscreen than a spray.

All sunscreen formulas—creams, lotions, sprays, sticks—will work equally well if used correctly, according to Dr. Zeichner. (So, how does sunscreen work, exactly? More details to come.) But you can't just spray a cloud of sunscreen across your body or haphazardly swipe on a stick: "You have to put a little concerted effort into your application technique," he adds. Consider his helpful guidelines: For sprays, hold the bottle an inch away from your body and spray for one to two seconds per area or until skin is glistening, then rub in thoroughly. Prefer sticks? Rub back and forth across each spot four times to deposit an adequate amount of product. (Related: The Best Spray Sunscreens That Won't Dry Out Your Skin)

Speaking of sunscreen application, it’s essential that you apply before going outdoors because it takes about 15 minutes for your skin the absorb the sunscreen and, thus, be protected. But this isn’t a one-and-done situation—you need to apply sunscreen throughout the day, too. So, how long does sunscreen last? It depends: As a general rule, you should swipe on more sunscreen every two hours, according to the AAD. Sweating or swimming? Then you should reapply more often, even if the product is water-resistant.

Myth: All sunscreens work the same way.

In order to answer the question, "how does sunscreen work?" you first need to know that sunscreens are split into two categories: chemical and physical. The former includes ingredients such as oxybenzone, avobenzone, and octisalate, which work by absorbing harmful radiation to dissipate it. Chemical sunscreen also tends to be easier to rub in without leaving a white residue. Physical sunscreens, on the other hand, “work like a shield” such that they sit on the surface of your skin and, with help from ingredients such as zinc oxide and titanium dioxide, deflect the sun’s harmful rays, according to the AAD.

Sunscreen vs. Sunblock

Now that you understand the basics of how sunscreen works, it’s time to tackle another oft-confused topic: sunscreen vs. sunblock. In theory, sunscreen absorbs UV rays and scatters them before they have the chance to damage your skin (i.e. chemical formula) while sunblock sits on the top of your skin and quite literally blocks and deflects the rays (i.e. physical formula). But back in 2011, the FDA ruled that any and all sun protection products, regardless of the ingredients they use, could only be called sunscreens. So, while people may still use the two terms interchangeably, technically speaking, there is no such thing as sunblock.

Whether you opt for a chemical or physical formula really boils down to a matter of personal preference: chemical ones tend to feel lighter, while physical formulas are a good option for people with sensitive skin. That being said, chemical sunscreens have come under scrutiny as of late, thanks to recent research conducted by the FDA that found that six common chemical sunscreen ingredients were absorbed into the blood at levels higher than the agency's safety threshold. It's unnerving to say the least, but it doesn't necessarily mean that these ingredients are unsafe—just that further research needs to be done. Unfortunately, however, that's not the only negative impact chemical sunscreens can cause. Research suggests that oxybenzone, one of the most commonly used ingredients in chemical formulas, can be damaging or "toxic" to coral reefs. This is just one more reason why natural or mineral sunscreens have continued to gain popularity and interest. (See also: Does Natural Sunscreen Hold Up Against Regular Sunscreen?)

At the end of the day, there's no denying that, "the risk of not using sunscreen outweighs the benefits of not wearing sunscreen," David E. Bank, M.D., a board-certified dermatologist based in New York, previously told Shape. Still concerned? Stick with physical formulas, as the FDA considers both zinc oxide and titanium dioxide to be safe and effective. (Related: The FDA Is Aiming to Make Some Big Changes to Your Sunscreen)

Myth: Your makeup has SPF in it so you don't need to use a separate sunscreen.

It’s smart to use makeup with SPF (the more protection, the better!), but it’s not an alternative to sunscreen (and neither are "sunscreen pills"). Think of it as a second line of defense, rather than your sole source of sun protection. Why? For starters, you're likely not applying your foundation or powder in an even layer across your entire face, says Dr. Zeichner. Plus, it would take a lot of makeup to get the level of SPF noted of the bottle, and most women simply aren't wearing that much, he adds. Moisturizer with sunscreen is OK, as long as it’s broad-spectrum and SPF 30 and you use enough (at least a nickel-size amount for your face).

Myth: Sunburns are dangerous, but getting a tan is fine.

A lobster red hue isn't the only indication of damaged skin. If you think achieving that gorgeous glow isn't a problem, guess again. "Any change in skin color—whether it's turning red or just darker—is an indication of sun damage," says Dr. Zeichner. Consider tan lines a warning sign that it's time to step up your sun protection, stat. On that note, does sunscreen prevent tanning? Yes. Sunscreen does, in fact, prevent tanning, but again, you need to be applying—and reapplying—it correctly and using enough. For the average-sized adult, “enough” is about 1 ounce of sunscreen (about the amount it takes to fill a shot glass) to evenly cover the body from head to toe, according to the FDA.

Myth: The SPF number is the only thing you need to look at when buying sunscreen.

There's a plethora of information to be found on a sunscreen label, though it can be confusing for most. In a 2015 study published in JAMA Dermatology, only 43 percent of people understood the meaning of the SPF value. Sound familiar? Don’t worry! You’re clearly not alone—plus, Dr. Zeichner’s here to help clear up this common confusion and then some. Here, what to look for when shopping for sunscreen and what each essential element means, according to Dr. Zeichner.

SPF: Sun Protection Factor. This only indicates the protection factor against burning UVB rays. Always look for the term "broad-spectrum," which indicates that the product defends against UVA and UVB rays. (You'll typically find this term prominently placed on the front of the packaging.)

Water Resistant: This can be on either the front or back of the bottle and refers to how long the formula can withstand water or sweat, which is typically 40 to 80 minutes. While it's not necessary to use a water-resistant option for everyday purposes, it's a must for the beach or pool or when you're going to be exercising outdoors. And the time claim should be the absolute longest you go before reapplying. To be safe, reapply any time you come out of the water. (Related:: Sunscreens for Working Out That Don't Suck—or Streak or Leave You Greasy)

Expiration Date: Contrary to popular belief, you probably shouldn't be using the same bottle of sunscreen you were using last summer. How long does sunscreen last? This depends on the particular formula, but a good general rule of thumb is to toss anything one year after buying it, or once it's expired. Most sunscreens will have an expiration date stamped on the bottom of the bottle or on the outer packaging if they come in a box. Why? "The chemicals in the lotion that block the sun decompose, making it ineffective," Debra Jaliman, M.D., a clinical instructor at the Mount Sinai School of Medicine, previously told Shape.

Non-Comedogenic: This means it won't block pores, so acne-prone types should always look for this term. (See also: The Best Face Sunscreen for Every Type of Skin, According to Amazon Shoppers)

Ingredient Panel: Found on the back of the bottle, this lists the active ingredients and is how you can tell whether a sunscreen is chemical or physical. The former includes ingredients like oxybenzone, avobenzone, and octisalate; zinc oxide and titanium dioxide are the most common physical blockers.

Usage Indications: These are required by a newly-passed FDA monograph, which note that, with proper use, sunscreen can protect against sunburns, skin cancer, and the signs of aging.

Alcohol-Free: Look for this when choosing a facial sunscreen, since alcohol can be drying on skin.

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