Windows and Tanning

Girl getting a tan through the window
Q: Can you get a tan through a window? My girlfriends and I have been arguing about this all day. We need to know!
A: Well, whomever among you were arguing that you CAN get a tan through a window is correct. Glass filters out some of the shorter wave Ultraviolet (UV) light, but allows longer wavelengths of UV light to pass through. This UV light can still cause sunburn and tanning of the skin, but it takes longer to generate the effect. Think of glass as a type of sunscreen: it protects you from some UV rays, but isn’t perfect protection.
It should also be noted that while glass does filter UVB rays (those responsible for burning the skin and tanning), the UVA radiation is not blocked and these rays are the ones responsible for the more long-term damage to the skin, such as cellular breakdown (aging effects) and even cancers.
Finally, another factor to consider is that the answer depends on the specific make-up of the glass being used. Some types of glass are made with specific UV coatings and UV filtering ingredients which can increase their effectiveness in filtering both UVA and UVB radiation. Sometimes this glass is marked with symbols and labeling to denote its UV-Protectant status.
However, its not usually easy to find this information unless you know the specifics of the construction of a building or the immediate environs. So, while you can say that glass provides some UV protection, you cannot be certain of the level of protection being provided.
{Note: Special thanks goes to Louis A. Bloomfield, author of “How Everything Works: Making Physics Out of the Ordinary” for the answer to this question, via the University of Virginia website.}
Photo: ArtFamily/Shutterstock
See also:
How tanning works
Is tanning dangerous?