Can You Really Get the Benefits (and Risks) of Sunlight Through a Window?

Ever find yourself soaking up the warm sunlight streaming through a window on a chilly day, daydreaming of summer and hoping for a touch of color? We’ve all been there.

A bright, sunny afternoon can lift your spirits, even when you’re tucked inside. But when it comes to sunlight, more isn’t always better.

Keep reading to discover how much of the sun’s effects — both beneficial and harmful — actually make it through glass.

Can you get a tan through a window?

It’s possible but unlikely, and it really depends on the particular window, how long you sit by it, and how strong the sun is.

Per the American Cancer Society, common residential, office, and vehicle windows block most UVB rays but allow some UVA rays to pass.

Older single-pane glass found in many homes offers less defense than newer windows, which are often thicker, double- or triple-paned, or treated with UV-blocking coatings.

In cars, windshields — laminated for safety — block a lot more UV than side windows and sunroofs, which are typically tempered glass.

Both UVA and UVB can harm skin, but they act differently:

• UVA reaches deeper skin layers and stimulates melanocytes to produce melanin, the pigment that darkens skin. It also contributes to wrinkles, premature aging, and some skin cancers.
• UVB affects the upper skin layers, causing sunburn and being a major contributor to skin cancer.

If you sit for extended periods by a window with strong direct sunlight, the UVA that penetrates the glass could give you a slight tan.

Aside from that subtle bronzing, remember that UVA is linked to sunspots and premature aging, and can harm blood vessels, nerves under the skin, and even damage DNA and immune function.

What about a sunburn?

Yes, you can get sunburned through a window. But again, it hinges on the type of glass, exposure duration, and the sun’s intensity.

Sunburn risk climbs with longer time in sunlight, especially when the UV index  is high. UV intensity is typically greatest around midday — roughly between 10 a.m. and 4 p.m.

What’s outside the window matters as well.

UV rays can reflect off surfaces and boost your exposure. Common reflective surfaces are water, sand, and snow.

So, if you’ve got a lovely view, you’re more likely to burn if you linger there long enough on a sunny day.

Can you still get vitamin D?

Unfortunately, no. Vitamin D — the “sunshine vitamin” — is produced when your skin encounters UVB rays, which most windows block.

In simple terms, UVB is absorbed by the skin and helps convert skin cholesterol into vitamin D.

If you aim to boost vitamin D from sunlight, the most effective method is direct skin exposure.

Experts suggest  exposing around a third of your skin (for example, shorts and a tank top) to sunlight for 10 to 30 minutes three times weekly.

People with darker skin require substantially longer sun exposure — anywhere from 30 minutes to several hours more — to synthesize the same vitamin D amounts as those with lighter skin.

This difference is due to higher melanin in darker skin, which reduces UVB absorption.

Still, don’t skip sunscreen. Darker skin can burn and develop skin cancer too. (Sunscreen doesn’t stop all vitamin D production; you can still make adequate amounts while protecting your skin.)

You can also increase dietary intake of vitamin D.

Can frequent driving really increase your risk for skin cancer?

Yes. As noted earlier, sunlight penetrates car windows, particularly side windows and sunroofs. People who spend a lot of time driving — drivers in particular — face a higher skin cancer risk.

In Australia this pattern has been nicknamed “cabbie cancers” because those who drive all day are more vulnerable.

The Skin Cancer Foundation reports that in the United States melanoma and nonmelanoma skin cancers appear more frequently on the left side of the body — the side where drivers sit.

The bottom line

Windows block some, but not all, of the rays that cause tanning and burning.

While you could, in theory, develop a faint tan if you spent most of your time in a sunny window, it’s not very practical. If you want a dependable glow, a spray tan is a safer option.