Do I really need to wear sunscreen indoors?

The importance of sunscreen has become abundantly clear over the last few years. Not only can it help prevent painful sunburns and premature skin aging, but wearing an SPF 15 or higher daily can also significantly reduce your risk of developing certain skin cancers. It’s why I’m diligent about applying sunscreen every time I go outside. But — and hear me out for a second — do I also need to be wearing sunscreen when I’m inside, minding my own business?

I thought it was a pretty wild idea, too, until I spoke with experts. It’s a really important question, says Ranella Hirsch, a Boston-based dermatologist. And the answer isn’t binary; it depends on what you consider your “indoor life.” “For instance, are you sitting in an office with a wall of windows or working at a desk facing forest sunlight?” asks Hirsch. If so, you’re going to want to consider a daily all-over application — especially if you are lighter skinned — no matter your exposure to the actual outdoors.

Naissan Wesley, a Los Angeles-based dermatologist agrees, noting that wearing sunscreen indoors simply is not a bad idea. “One, it’s good to get into the habit of wearing [it] each day so that we don’t forget to apply it before inadvertently going outdoors,” she says. But it’s not just about forming good habits; SPF is important for protection inside, too. To suss out just how crucial it really is, I asked dermatologists for more info on the benefits of wearing sunscreen inside, the risks of going without it, and their tips on how to best protect your skin indoors.

Seriously, should I wear sunscreen indoors?

We now know the short answers are “yes” and “why not?” But let’s talk more about the logic behind that. Unless you’re spending all of your indoor time in a windowless room, you’re not completely protected from the sun. That’s particularly true when talking about the effects of UVA (ultraviolet A) rays, which Hirsch says can penetrate glass, unlike UVB rays. While, she notes, UVB rays are primarily responsible for sunburns, UVA rays can cause significant damage to the skin — like premature aging and even some types of skin cancer. Just like when you’re outside, sunscreen plays a key role in lowering these risks.

“UVA is a wavelength that penetrates deeply and causes a lot of damage on its own, including through glass,” Hirsch says. According to the Skin Cancer Foundation, UVA is everywhere. In fact, UVA rays account for up to 95% of the ultraviolet radiation that reaches the earth. “These rays maintain the same level of strength during daylight hours throughout the year,” the organization notes on its website. “This means that during a lifetime, we are all exposed to a high level of UVA rays.”

Even on the cloudiest of days, wearing sunscreen indoors is wise. While most of us are probably familiar with sunscreen’s ability to act as, well, a screen from the sun, you might not have realized it also protects against other types of harmful exposures. “Sunscreen, particularly the mineral sunscreens, can also act as a barrier to environmental pollutants and damage, as well as from blue light emitted from computer screens and electronics,” Wesley says.

Environmental pollutants come in many forms, including CFCs (chlorofluorocarbons) like perfumes and aerosols, carbon monoxide, and even plastics. A 2019 study published in the Journal of the European Academy of Dermatology and Venerology, showed damage from environmental pollutants can cause skin issues ranging from acne, to eczema, to some types of skin cancer.

As for technology, “despite blue light not causing the skin to physically burn, it is still extremely harmful,” says Stacy Chimento, a dermatologist at Miami’s Riverchase Dermatology. Not only can blue light cause premature aging and increase melanin production in the skin (which leads to age spots), but Chimento says it can also lead to sagging skin “from a decrease in collagen due to its formation of free radicals.” It’s true: A 2015 study published in Oxidative Medicine and Cellular Longevity showed blue light decreases carotenoids — a type of antioxidant that protects your skin — which can lead to a boost in free radicals, which are molecules that damage skin cells and lead to wrinkles, fine lines, and dark spots.

What type of sunscreen should I wear indoors?

The rules for applying sunscreen indoors aren’t much different than when you’re hitting the beach — and in both cases, Wesley says it’s important to choose a formula that protects against both UVA and UVB rays.

“This is particularly true of the physical blocking sunscreens that contain mineral ingredients, such as zinc oxide and titanium dioxide, that form a physical barrier on our skin surface,” she notes. She recommends a broad-spectrum sunscreen — meaning it blocks both types of ultraviolet rays — that is mineral-based and SPF 30 or higher.

Hirsch agrees, adding that regular UVA and UVB sunscreen does not protect against high energy visible (HEV) light from the sun. “The protection [from a broad-spectrum sunscreen] comes in the form of the pigmentary oxides of the tints in tinted products, which is why you often see tinted sunscreens recommended for those with pigmentary conditions.”

Also important to note: While you might hear the terms “mineral sunscreen” and “chemical sunscreen,” Hirsch says those references are technically out of date. Instead, think of them as organic (mineral) and inorganic (chemical). Whereas an organic sunscreen uses zinc oxide or titanium dioxide to block UV rays, inorganic sunscreens rely on chemicals to more or less filter UV rays.

How often do I need to reapply sunscreen when I'm indoors?

Sunscreen reapplication when you’re swimming or sweating it out in the sun is crucial, but do you need to repeat the slathering process throughout the day inside as well? “If you are sitting indoors (not near windows), you are likely okay with one application of sunscreen in the morning,” Chimento says. “However, if you are sitting in a room that receives lots of sunlight or are using technology for extended periods of time, it may be beneficial to reapply sunscreen every three to four hours.” And if you exercise indoors, you’ll likely sweat off at least some of the SPF, so be sure to reapply after you’re done.

The bottom line

While you don’t need to go full-on “day at the beach” with your indoor sunscreen application, you’ll definitely want to consider your daily exposure to blue light (and that corner window spot at work that you love oh-so-much). Choose a tinted moisturizer with broad spectrum SPF 30 (like this one from bareMinerals) or even a primer that goes on under your makeup (yours truly j'adores this one from SuperGoop!) if you wear any. After that, you just need to nail down a solid pair of computer glasses and you’ll be an UV rays blocking machine.