Can you get a suntan through a window?

We all know that too much exposure to sunlight can cause skin cancer, but not enough sunlight can cause Vitamin D deficiency and weak bones.

What about sun exposure through a window?

The sun emits UVA, UVB, and UVC rays.  Most UVC rays are filtered out by the earth’s atmosphere.  Windows filter out about 97% of UVB rays, but  do not filter out all UVA rays.  So you can still tan through a window!  Sitting next to a window is like wearing SPF 30 sunscreen,  as many rays do get filtered out, but you can still get tan with long enough exposure.

One interesting study found that 74% of patients with skin cancer had tumors on their left sides, which is the window side of  cars in North America!  Modern cars now have a plastic layer bonded between two layers of glass, and block out all UVB and 80% of UVA rays, making sunburn less likely.

What about vitamin D?  Vitamin D is produced in our skin by UVB rays.  But glass windows block this out.  That means that you would get little, if any, Vitamin D from sitting by a window.

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