Does SPF 100 Sunscreen Give You 100-Percent Protection Against the Sun?

Let's face it: sunscreen labels are confusing. In particular, there’s some collective head-scratching around whether a sunscreen with a higher sun protection factor — say, SPF 100 — actually means more protection from the sun when compared to another sunscreen that only features SPF 30 or 50. Surely it's logical to just use the highest SPF you can find, right? Well, yes and no. The protection offered at different SPFs is a little more complicated than that, especially when human error is factored into the mix.

As a reminder, the sun protection factor (SPF) is only a measure of how well a sunscreen protects the skin against UVB rays. "The sun emits UVB, UVA, HEV (High Energy Visible Light), and IR (Infrared) rays," says Loretta Ciraldo MD, a Miami-based board-certified dermatologist. "UVB rays are the burning rays that penetrate into the skin's top layer and are responsible for the redness, peeling, and pain that accompanies sunburn," she adds.

A sunscreen's protection may not be obvious from the SPF number on the label, though. The idea that an SPF 100 means you're 100 percent protected from the sun is categorically untrue. And if the difference in the level of protection between SPF 30 and SPF 100 is only two percent, does that really make a transformative difference to your skin? After all, no sunscreen is 100 percent effective. And what about Korean sunscreens, which have a "PA" rating?

To get to the bottom of these theories, assumptions, and (possibly) misconceptions, we're breaking down exactly when you need to consider when choosing a sunscreen and whether higher does actually mean better. We spoke to dermatologists and cosmetic chemists to get their expertise on the big question: When it comes to SPF, how high is high enough to keep our skin safe in the sun?

• Loretta Ciraldo MD, a board-certified dermatologist and founder of Dr. Loretta Skincare based in Miami, Florida.
• Joshua Zeichner MD, a board-certified dermatologist and the director of cosmetic and clinical research of dermatology at Mount Sinai Hospital in New York City.
• David Kim MD, a board-certified dermatologist in New York City.
• Laura Lam-Phaure, a cosmetic chemist based in Los Angeles.
• Darrell Rigel MD, a board-certified dermatologist and clinical professor of dermatology at New York University Langone Medical Center in New York City.

• What do SPF numbers actually mean?
• Does higher SPF actually protect your skin better?
• Are there downsides to using a higher SPF?
• If it's not broad-spectrum, don't buy it
• What about Korean sunscreens?
• So, is SPF 100 better than SPF 30?
• How to create the perfect sun-care routine

It would seem intuitive that a higher SPF sunscreen would mean more protection, right? Sort of, but it's more nuanced than that.

Let's first break down how the SPF system works: "SPF 15 guards against 93 percent of UVB rays, SPF 30 protects against 97 percent, SPF 50 is about 98 percent, and SPF 100 blocks 99 percent," Joshua Zeichner MD, a board-certified dermatologist from New York City, tells Allure. Another way to look at it is this: "A product with SPF 15 will give you the same amount of UV exposure after 15 minutes that you would get after one minute being outdoors unprotected," he says. "The greater the SPF number, the more protected you are against sunburn," he adds.

In other words, you get double the sun exposure when you opt for SPF 15 instead of SPF 30. To give you a visual, "a product with an SPF 30 means that you get the same amount of sun exposure after 30 minutes outside as you would get if you were unprotected outdoors for one minute," Zeichner adds. Since no product can be 100 percent effective, there's not a whole lot of room for improvement after 97 or 98 percent, but researchers were determined to find out if using SPF 100 made a tangible difference in reducing sun damage.

For the most part: yes. Those in favor of high SPFs often refer to a 2018 study in which a group of 199 adult participants, researchers had each person use a different SPF on each side of their face — SPF 50 on one side and SPF 100 on the other side — before spending a day in natural sunlight. The following day, the researchers measured the sun damage present on each side of the participants' faces. Turns out, the SPF 100 (which was Neutrogena Ultra Sheer Dry-Touch Sunscreen Broad Spectrum SPF 100+ in case you want to snag some) really did make a difference. 

"Didn't matter your skin type, age, or gender, the SPF 100 was always better," says Darrell Rigel MD, a board-certified dermatologist and clinical professor of dermatology at New York University Langone Medical Center and an author of the study, which was funded by Johnson & Johnson Consumer Inc. Rigel and his co-authors found that 55 percent of the participants were more sunburned on the SPF 50 side than they were on the SPF 100 side, according to the findings published in the Journal of the American Academy of Dermatology.

"People were about 10 times more likely to burn on the SPF 50 side than the SPF 100 side," Rigel says. Given the results, the researchers concluded that SPF 100 is "significantly more effective in protecting against sunburn than SPF 50." That said, there's more to choosing a sunscreen than an SPF number. Read on for the words you should always look for on your label.

There is a catch (well, several) when it comes to higher SPF. First, while an SPF above 60 may offer greater protection again UVB, due to photochemistry, it typically has less UVA protection, Dr. Ciraldo tells Allure. And, trust us, you should be worried about both. 

"UVA rays penetrate even more deeply and are responsible for most skin aging, hyperpigmentation, damage to collagen fibers, and more aggressive skin cancers including melanomas," Dr. Ciraldo notes. It's for this reason, she says, that the FDA is now strongly considering guidelines to make 60 the highest SPF you can buy.

There's also the danger that a higher SPF number will impart a false sense of security. "People believe that if they have an SPF 100 they have significantly increased protection so they can stay out in the sun for longer without reapplying their sunscreen," says Dr. Ciraldo.

Another reason she isn't a fan of SPF 60 plus sunscreens is "the higher levels of chemicals," says Dr. Ciraldo. Concerns around avobenzone have been bubbling up for some time, with the FDA still reviewing its safety alongside 11 other chemical filters that absorb into the body. That said, cosmetic chemist Laura Lam-Phaure doesn't believe there is reason for alarm. 

"A higher SPF doesn’t necessarily correlate with having an increased concentration of chemical actives like avobenzone," she says. "In an optimal sunscreen formula, photo-stabilizers, emollients and antioxidants all contribute to the SPF value, spreadability, and stability of the final formulation," she adds.

When choosing a sunscreen to purchase, all of our experts recommend looking for the words "broad spectrum" on the bottle.

"This means that your sunscreen offers both UVB and UVA protection," says board-certified dermatologist David Kim, M.D. It's one way to ensure that you get adequate UVA protection because not all sunscreens have PA ratings (more on that later) in the US, he adds.

In short, even if you're using a high SPF sunscreen, if it isn't broad-spectrum, you're better off applying a lower-strength sunscreen that is, says Dr. Zeichner. "I would rather you choose an SPF 15 product that protects against UVA rays and UVB rays as opposed to a higher SPF that doesn’t give you UVA protection," he adds.

According to Lam-Phaure, South Korean sunscreen formulas are advancing at a fevered clip compared to the U.S. "The FDA considers sunscreens over-the-counter drugs, so formulators are limited with what ingredients they can use," Lam-Phaure tells Allure. "The addition of any new active ingredients to the Title 21 Monograph, which regulates these drugs, would require extensive testing," she adds. Yet Asian sunscreen formulators now have filters like Tinosorb at their disposal, which delivers a double-whammy by protecting against both UVA and UVB rays. "In fact, the last time the FDA made any decisions regarding sunscreens was in the 1970s," says Lam-Phaure. "It's unlikely that'll we see new approved UV filters any time soon due to a lack of FDA funding for the cosmetics sector, as well as a lack of data," she notes.

Apart from being famously featherlight, what makes K-beauty sunscreens so special is their PA (Protection Grade of UVA Rays) rating in addition to the standard SPF, says Dr. Ciraldo. "This number reflects the amount of protection from persistent pigment darkening (PPD) and measures how much UVA a person can be exposed to without tanning," she says, adding that she hopes Western countries like the U.S. will adopt the system in the future.

The PA system ranges from PA+ to PA++++, so "the greater the number of plus signs, the better the level of protection against UVA rays," says Dr. Zeichner.

Largely, yes, but the clearer consensus among dermatologists is that a sunscreen that boasts both UVA and UVB protection is always the best way to go. And experts confirm that all of this is null and void if we don't apply sunscreen correctly in the first place. 

"People typically only apply 25 to 50 percent of the rated amount," explains Dr. Zeichner, who adds that if you're not diligent with the application, the SPF value gets diluted out because it’s being spread too thinly over the skin. So, if you're using an SPF 30 sunscreen, you might only be getting SPF 15 in reality. Therefore, he does recommend a higher SPF, but one with UVA protection built-in. "There's less of a drop-off in protection levels with an SPF 100 than there is with an SPF 15, even if you're not applying enough of it," Dr. Zeichner concludes.

At the end of the day, the best sunscreen is the one that you're actually applying, echoes Dr. Kim. “If you have an SPF 30 sunscreen that you love and will use consistently throughout the day, that’s much more effective than choosing one with an SPF 100 that you don’t like and apply only once,” he says.

The good news: any sunscreen is better than no sunscreen at all. That said, there are small ways to optimize your sun protection. 

Regardless of SPF, always choose a sunscreen with "Broad Spectrum" written on the label to make sure you're getting protection from UVA rays as well. "UVA rays are responsible for early skin aging and skin cancer, while UVB rays are responsible for sunburn," says Zeichner.

"Prior to [the aforementioned] study, I commonly recommended broad-spectrum sunscreen with higher SPFs if people are going to be outdoors, especially if for prolonged periods of time, so I will continue to do so," says Shah.

"Sunscreen is your last step in the morning," Jeannette Graf, M.D., a board-certified dermatologist in Great Neck, New York, previously told Allure when explaining how to properly layer your skin-care products for maximum effectiveness. "It sits on top of your skin, so if it goes on first, it prevents other ingredients from penetrating."

Keep in mind that the effectiveness of your SPF, no matter how high it is, depends on how thoroughly and how well you apply it. "People typically only apply 25 to 50 percent of the rated amount. So if you're using SPF 30 sunscreen, in reality, you might only be getting SPF 7," explains Rigel.

A good rule of thumb: For your face, you should be using a quarter-sized dollop, and another squeeze (approximately the size of a shot glass) for your body, says Zeichner. And don't skimp on additional measures like wearing protective clothing, staying in the shade when possible (especially if you'll be outdoors for an extended period of time), and paying close attention to how the sun may be impacting you — for instance, if you start to feel the inklings of sunburn or, worse, start to show symptoms of sun poisoning, especially if you have a dermatological condition or sensitive skin.

On top of that, reapply every two hours and pay attention to oft missed spots like eyelids, scalp, and hairline. "The amount of UV light that penetrates into the skin is significantly more than you would expect based on the label on the bottle if you are not using it correctly," Zeichner says.

You've heard it a million times before, but we'll say it again: Always wear sunscreen, and — usually, at least — the higher the SPF, the better.

Read more stories about sun protection:

• This Is How the Sun Causes Skin Cancer
• The Best Sunscreens, According to Allure Editors
• What Does Melanoma Look Like? A Visual Guide
• The Ultimate Guide to Skin Conditions for Brown & Black Folks

Now, find out the science of sunscreen: