All of us know that too much direct sunlight on our skin is not good for us, though we don't always act in accordance with that fact. While a little sun is great for increasing our production of vitamin D, for improving our mood and for giving us a healthy-looking glow, too much of it can cause sunburn, make you look wrinkly in older age and drastically increase your chances of getting skin cancer.
But the question is whether or not sitting by a window will have the same effects as sitting outside? Can you still get sunburn? Will you still produce more vitamin D?
Can UV Rays Be Harmful Through Glass?
The most important question to ask is whether or not those UV rays can harm you through a window. If you're sitting at your computer by a window right now, then are you getting harmed in any way by the light coming through it?
Unfortunately the answer is a yes – UV rays do come through glass and can still cause you damage. That said though, it does block some of the sun's rays depending on their wavelength…
Specifically windows will block all of the 'UVB' while still letting 'UVA' come through. UVB is the 'shorter wave' light and is what's primarily responsible for sunburn and skin cancer. It's also what the SPF in your sunblock is telling you it can block. UVB only makes it some of the way through your skin (just into the epidermis) and is also blocked by water when you're swimming beneath the surface.
Meanwhile though, UVA rays – with the slightly longer wave – can still pass through glass and can still cause problems. This is the type of light used in tanning beds and is able to penetrate the skin more deeply through the epidermis and into the dermis. This actually makes it worse when it comes to ageing your skin. Take a look at someone who's driven a truck for a living their whole life and you'll probably see that one side of their face is more wrinkled and lined that the other. Same goes for you if you have a window by your desk on one side!
UVA rays can also contribute to your risk of skin cancer, so don't assume that sitting by the window is completely safe. In fact no sunblock will even protect you completely from UVA – SPF only refers to UVB and says nothing of UVA. If you want to get a sunblock with increased protection against UVA then you should use one that says 'full spectrum'. Mineral sunblocks are particularly useful.
Health Benefits of Sitting by Windows
So if sitting by a window still exposes you to some of the harmful effects of the sun, does that mean you also get the positive benefits from it too?
Fortunately, the answer here may also be yes. Sitting by the window will allow UVA light to pass through and in one study it was found that UVB phototherapy over a 6 week period was enough to boost vitamin D levels. Do bear in mind though that most of us get enough vitamin D through our diets and through the sun exposure we get just from walking to work etc.
What about tanning? Well, seeing as windows provide a similar type of protection to a high UPF sunblock, your ability to tan is also similar. You're hardly going to go brown overnight, but if you allow yourself prolonged exposure you'll find that you do gradually start to go darker. In bright enough sunlight over a long enough period of time it is even possible to burn.
You can get some benefits from sitting by a window then and you may find that it's sufficient to help boost your mood, your testosterone and your vitamin D. More likely though, if you are spending prolonged periods by a window you could be doing yourself harm through exposure to UVA rays.
So what can you do to protect yourself?
One option is to use a mineral-based wide-spectrum sunblock, though most people aren't going to want to use sun-blocks while indoors. A better option is to simply ensure that you change position from time to time so that you alter the side of your face you're exposing to the sun.
If you're really worried though and changing sides isn't an option, you should look into getting a window designed to block more UV rays. Special window UV films can block up to 99.9% of the sun's rays and should help you to protect your skin adequately.