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The Ultimate Guide to Sunscreen

May 28, 2021 By Ashley Abramson
Woman on beach putting sunscreen on her face.

Summer’s just around the corner –– and that means it’s time to get out the sunscreen. Experts recommend people protect their skin with SPF year-round (yes, even on cloudy days!). But now that you’ll likely be spending more time outdoors in direct sunlight, it’s a great time to start thinking seriously about your sunscreen strategy.

Why wear sunscreen?

Not only does slathering on that SPF prevent premature signs of aging (like wrinkles and age spots), but protecting your skin from harmful rays also decreases your risk of skin cancer. According to the Skin Cancer Foundation, habitual, daily use of SPF 15 can reduce a person’s risk of squamous cell carcinoma by around 40% and melanoma by nearly half.

Sunscreen works by preventing the sun’s harmful UV rays from reaching (and damaging) your skin. The American Academy of Dermatology recommends everyone (with the exception of infants under six months) wear broad-spectrum, water-resistant sunscreen of SPF 30. Sounds pretty straightforward, right? Well, not exactly.

Not all products are created equal –– and reading the label of a sunscreen bottle can feel like decoding another language. What do all those complicated words on the label and ingredient list mean, and more importantly, how do they affect your skin and overall health?

Here’s a rundown of common lingo you’ll find on a sunscreen bottle –– and how important it all is to your health, this summer and beyond.


SPF is the level of protection a sunscreen offers against UVB rays. In general, higher SPF equals greater protection, but a higher SPF number isn’t always better. According to the American Cancer Society, the difference in protection is smaller the higher the number is. For example, SPF 15 sunscreens are thought to filter out around 93% of UVB rays, SPF 30 products filter about 97%, and SPF 50 about 98%.


Broad-spectrum sunscreen protects skin from both UVA and UVB rays. Because of its comprehensive protection, it’s the type of sunscreen recommended by the American Academy of Dermatology.


Sunlight consists of two different kinds of rays. UVB rays, also called “burning rays,” are the type of rays that cause your skin to burn and also lead to skin cancer. UVB rays can be filtered though and do not penetrate glass.


UVA rays or ultraviolet A rays — nicknamed “aging rays” — can cause premature skin aging, including wrinkles, sagging, and age spots. Overexposure to UVA rays, which penetrate more deeply into a person’s skin than UVB rays, can also increase a person’s risk of skin cancer. This type of ray can pass through window glass, which is why experts recommend sunscreen even if you don’t go outside –– like if you’re driving or sitting by a window at home or in your office.

Physical sunscreen

Physical sunscreen ingredients, also called mineral sunscreen, uses minerals titanium dioxide and zinc oxide to block the sun’s rays before they ever penetrate your skin. This type of sunscreen sits on top of the skin, so it’s more prone to wearing off; however, it’s photostable which means it won’t degrade and become ineffective when in contact with sunlight. Physical sunscreens include ingredients like zinc oxide and titanium dioxide.

Chemical sunscreen

Chemical sunscreen ingredients, such as avobenzone or oxybenzone, work differently –– they absorb UV rays before they can harm your skin. This type of sunscreen absorbs into the skin, so manufacturers often include it in skincare products and makeup. Chemical sunscreens include ingredients like oxybenzone and avobenzone.

Both physical and chemical sunscreens are effective, so it comes down to personal preference. If you have to pick, opt for physical sunscreen for outdoor activities and chemical sunscreen for everyday, year-round use.

Water resistant

Water resistance is one of the essential recommendations by the American Academy of Dermatology –– but keep in mind, water resistant doesn’t mean waterproof. Instead, water resistance means the sunscreen’s SPF is maintained –– and the sunscreen will be effective –– for up to 40 minutes in water. Extra water-resistant sunscreen is effective for twice that, or 80 minutes. If that period of time passes, reapply!

The American Cancer Society recommends reapplying sunscreen at least every two hours, and more frequently if you’re swimming or sweating, or if you’ve wiped yourself off with a towel.


Sunscreens labeled “sport” are usually just water-resistant, since active people are more likely to sweat. If you’re active (or just prone to sweat), choose a sunscreen that’s either water resistant or extra-water resistant.


Babies under the age of six months should avoid sunscreen and instead be kept in the shade and use protective clothing from the sun. Sunscreen can be used if shade or adequate clothing is not available, but should be used sparingly. While there’s no FDA designation for “baby” sunscreen,” usually this means the product is physical and not chemical to avoid irritating a baby’s sensitive skin. It’s worth noting that adults who’d rather avoid chemicals can use “baby” sunscreen, too.

Other ways to protect yourself

Now that you know how to choose (and use) a sunscreen for optimal protection, keep in mind sunscreen can’t fully protect you from potentially harmful rays. If you’re spending time outdoors, protect your skin by wearing appropriate clothing, like sunglasses and a wide-brimmed hat. And as much fun as it is to hang out in the sun, try to stay in the shade as much as possible!

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Ashley Abramson

The One Medical blog is published by One Medical, a national, modern primary care practice pairing 24/7 virtual care services with inviting and convenient in-person care at over 100 locations across the U.S. One Medical is on a mission to transform health care for all through a human-centered, technology-powered approach to caring for people at every stage of life.

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