Sun Risk From Side Windows

If you spend a lot of time in a car, be aware that side windows do not protect well against ultraviolet­ A (UVA) radiation. That is the kind of radiation that is mainly responsible for skin cancer and cataracts.

  • Clear glass filters out nearly all ultraviolet ­B (UVB, causes sunburns, as well as contributing to skin cancer).
  • But, depending on how the glass is made and treated, varying amounts of UVA pass through.

An investigative study found that front windshields better protected against UVA than side windows1.

  • Using a handheld UVA light meter, the researcher tested 29 cars from 15 manufacturers on a cloudless day in Los Angeles.
  • They found that front windshields blocked, on average, 96% of these harmful rays (with a range of 95% to 98%).
  • Side windows, however, blocked only 71% (44% to 96%).

This helps explain why other studies have found an increased prevalence of left-­sided cataracts and of skin cancer (including malignant melanoma) on the left side of the face and on left arms in countries where the steering wheel is on the left side of the car. In countries where the steering wheel is on the right side, more cases occur on the right side of the body.

  • The front windshields are required to have a clear plastic layer in between two panes of glass. This is to lessen damage in case of shattering. And it provides excellent UVA protection. It is similar to sunscreen with an SPF of about 50.
  • In contrast, side windows are typically not laminated but rather are composed of single­ pane glass, which “may or may not have a high level of UVA­-blocking polymers and other protective components,” according to the study.

Don’t assume tinted windows block more UVA or that newer or higher ­end car models provide more protection. In fact, Porsche and BMW models were among the cars with the worst side­-window protection. 

For the most protection, when the sun is at your side, keep the window up and flip the front visor to the side. In addition, use a broad-spectrum sunscreen and wear long sleeves and sunglasses. You can also have the side windows treated to block nearly all UV rays.