How Bad Is It Really to Not Wear Sunscreen Indoors?

When it comes to sun safety, we've (thankfully) come a long way since the days when it was the norm to slather on oil and sunbathe, or hop into a tanning bed to hone a sun-kissed skin tone.

A 2015 National Health Interview Survey found that 71 percent of Americans wear sunscreen almost every time they go outdoors on a warm, sunny day. That's up from only about 30 percent in 2005, according to a November 2011 review in the ​Journal of the American Academy of Dermatology​.

But despite the overall rise in sun savvy, some blind spots persist even today. Chief among them: the mistaken belief that you can forgo sunscreen when you're indoors.

"UV radiation from the sun can penetrate most home and car windows," says Oma Agbai, MD, assistant professor of dermatology and director of Multicultural Dermatology and Hair Disorders at the University of California Davis. This means that even if you're behind closed doors, rays of light can harm your skin.

And if the coronavirus pandemic has you working from home, chances are you're spending more time indoors than if you were commuting. So even if you'd ordinarily apply sunscreen before heading to work, you might be passing up this crucial skincare step now that you're staying in.

But what really happens if you skip your SPF fix when you're inside? Does it actually have that much of an effect on your health and appearance? We asked dermatologists to weigh in.

There are two types of ultraviolet radiation: UVA and UVB rays. "They each penetrate different levels of the skin and affect different structures in the skin," Dr. Agbai says.

According to the American Cancer Society, UVB rays target superficial skin layers. They damage the skin's DNA, are the primary cause of sunburn and cause most skin cancers.

Here's the good news: A September 2009 study in ​Photodermatology Photoimmunology and Photomedicine​ revealed that window glass filters out deadly UVB rays.

The not-so-good news? Windows aren't very effective at blocking UVA rays, which penetrate deeper layers of the skin. The same study determined that 74 percent of UVA rays are transmitted through glass.

"UVA radiation is responsible not only for skin cancers but also for collagen degradation resulting in photo-aging," says Tarannum Jaleel, MD, dermatologist at the Duke Dermatology Clinic.

These rays penetrate the dermis, damaging collagen and elastin, and trigger accelerated aging. Think: sagging, wrinkles, leathery skin and hyperpigmentation.

Get this: It's not just sunlight that poses a danger to your skin. Blue light from overhead LED lights and electronic devices (like your phone, laptop and television) can wreak havoc, too.

"It penetrates the skin, increasing the generation of free radicals, which break down collagen and elastin, leading to premature aging," Dr. Agbai says.

A December 2018 study in the ​Journal of Biomedical Physics & Engineering​ indicates that as little as one hour of exposure to blue light can cause skin damage.

The bottom line is, just because you're staying in doesn't mean you're off the hook for sunblock — and you should smooth it onto all uncovered skin, rather than only your face.

"Put it on your face, ears, neck, chest and arms, if they're exposed," Dr. Agbai says. "Apply enough to create a film on your skin that you have to rub in."

The kind of sunblock you use matters, so here's what to look for: "Wear a broad-spectrum sunscreen with an SPF of at least 30, which blocks both UVB and UVA rays and offers partial coverage against blue light," Dr. Agbai says. "Sunscreens containing iron oxide provide more complete protection against blue light and are therefore recommended for people with disorders of hyperpigmentation such as solar lentigos or melasma." (FYI: All tinted sunscreens, as well as some non-tinted varieties, contain iron oxide.)

If you'll be spending time outside, aim to reapply every two hours, per the Skin Cancer Foundation.

But a small November 2018 study in the ​Journal of Dermatological Treatment​ of 20 indoor workers suggests that you might be able to stretch the time between applications if you're staying in. Study participants put on one gram of sunscreen in the morning, and after an eight-hour workday with minimal outdoor time, the sunscreen had diminished by just 28 percent.

Avoiding direct sunlight will reduce UVA exposure, Dr. Agbai says. If sunbeams are streaming through the window, close the blinds or move to a different area until the sun has shifted.

To counteract the harmful effects of blue light, choose lightbulbs described as "warm white" rather than "cool white" or "daylight." Consider purchasing a blue light filter for your computer to limit the amount of blue light emitted, and download a blue light filter app, which tints your phone's screen to neutralize blue light.

Eh, it's moderately bad, but not terrible.

"Based on what we know now, light from electronic screens and UVA radiation through the window ​can​ have an effect on your skin," Dr. Agbai says. "Wearing sunscreen inside is fairly important in staying safe and skin cancer-free — especially these days, where people are spending more time in home offices and not venturing out as frequently."

Let's put it this way: On a 1-10 risk scale, where 10 is sunbathing on a scorching day sans SPF, and 1 is not wearing sunblock in the middle of the night, Dr. Agbai pegs skipping sunscreen indoors at a 4 or 5.

Still, since it keeps you healthy and looking youthful, and only takes a couple of minutes to apply, we say play it safe and get your SPF on!