You might think you've got your sun care routine down pat—apply a broad-spectrum sunscreen every time you head outside and reapply regularly. After all, you know that you need to protect yourself from the sun's harmful ultraviolet (UV) rays when you're outdoors.

But what if you're spending the day inside? Maybe you plan to work at your desk all day, or you'll be traveling for hours inside a car, plane, or train. You may be wondering, "Do I need sunscreen indoors?"

The short answer: Yes.

Before you pass on the SPF at home, here's what you need to know.

Why Do I Need Sunscreen Indoors?

It may seem like you're safe from the sun's UV rays within the four walls of your home or office. But the truth is that although window glass may filter some UV rays, it doesn't block all of them.

According to the Skin Cancer Foundation, UVB rays—the type responsible for sunburns— can't pass through glass, but UVA rays can. UVA rays can penetrate deeper into the skin and are responsible for premature aging: think wrinkles, brown spots, and leathery skin. They can contribute to skin cancer, too.

So, if you're at your house, work, or gym sitting by a window and soaking up the sun, you're exposed to UVA rays. The same goes for traveling in a car. Although car windshields are often treated to filter out UVA rays, other windows in the car—the side, back, and sunroof windows—are not. UVA rays can also pass through windows on airplanes and other vehicles, too.

How to Protect Your Skin While Indoors

UVA rays are present year-round and make up roughly 95 percent of the UV radiation that reaches Earth. This means that you're exposed to a lot of UVA radiation over your lifetime. And given that sun damage accumulates over time, it's important to protect your skin, even when you think your burn risk is low. At some point, you'll likely find yourself in a situation where you might wonder, do I need sunscreen indoors? When you do, err on the side of caution and take care of your skin.

One of the easiest ways is to apply broad-spectrum SPF 30+ sunscreen every morning. You won't miss the extra minute it takes, and it could protect you from long-term damage. Your strategy for refreshing your sunscreen will depend on where you're sitting while inside. If you're seated right next to a window, reapply every two hours. You can also install UV-blocking window treatments, whether it's hanging curtains or applying UV-blocking film to your windows at home or in your car. Your eyes may thank you for this, as well.

It can be tempting to skip the SPF as you rush to meet your ride or leave for the airport, but be especially sure to apply sunscreen before traveling by car or plane. You can also protect yourself by wearing sunglasses or a hat. If you're sitting on the sunny side and feel like you're burning up, put on a long-sleeve shirt or other piece of clothing, especially if you're flying. UV rays intensify with altitude, according to the World Health Organization.

Know Your Options

If you're thinking you'd prefer to skip the thick, greasy sunscreens when working or traveling, know that you can save those for outdoor activity. There are lighter options such as UV Clear Broad-Specrum SPF 46 that go on like a moisturizer and work well with any makeup you might wear. When it comes to skin health, you have many options to protect yourself comfortably, indoors and out.

Finally, visit your Dermatologist regularly. Not only is it an opportunity for your doctor to conduct a full-body skin exam, but it's a good time to talk to them about any concerns you may have and get recommendations on the best products to use. They'll be happy to share their expertise and help you on your journey to healthier skin.