A lot of people know by now that you can’t get a sunburn through window glass, whether it’s on your car or whether it’s at home in your room with a lot of windows or even in your office. That’s because window glass blocks all the UVB rays which are they rays that cause sunburn and do contribute to skin cancer. But that window glass has no effect on UVA rays, UVA rays are the rays that cause premature aging of the skin and also are important in contributing to skin cancer. A question that I’m often asked is, if I’m in my room, with a lot of windows and I also have a lot of mirrors, can the mirrors additionally reflect the UV light and cause more damage and the short answer is, those mirrors will reflect all the UVA light but none of the UVB light. Let’s take a look at this. Most mirrors are just a piece of flat glass with a coating on the back of aluminum. Some of them have silver, but most of them today are aluminum. We already know that when the light goes through the glass all the UVB is absorbed, so even if you’re at home with your windows open and UVB comes in once it hits the mirror it’s going to be absorbed by the glass, the UVB is gone. But aluminum, the backing on the mirror, is a very effective reflector of UVA and we also know that the glass doesn’t stop the UVA so that’s the reason the mirrors reflect almost all of the UVA light and none of the UVB light. So, mirror, mirror on the wall, which UV do you reflect to all? UVA my dear, and that just one more reason to wear sunscreen every day, indoors or out, with an SPF of between 15 and 30 and UVA protection.