It's easy to assume you're protected from the sun inside a car. You're partly right: the windshield blocks most ultraviolet (UV) light. The side windows are a different story, and hours of commuting add up.
Windshields and side windows are not the same glass
Windshields are laminated: two layers of glass with a plastic layer between them, and that plastic absorbs most UV. Side and rear windows are usually single-layer tempered glass. It stops most UVB (the burning rays) but lets through a share of UVA, which reaches deeper into the skin and causes aging and skin cancer.
A 2016 study of 29 cars in JAMA Ophthalmology measured this directly. Windshields blocked about 96% of UVA on average. Side windows averaged about 71%, and ranged from as little as 44% to 96% depending on the car.
What long exposure looks like
The clearest example is a 2012 case in the New England Journal of Medicine: a man who had driven a delivery truck for 28 years had far more sun damage on the left side of his face, the side next to his window, than on the right. Doctors described thickened, wrinkled skin and other signs of chronic UVA exposure on that side only.
Larger studies point the same way. In the US, where drivers sit on the left, skin cancers are more common on the left side of the body than the right, and researchers link part of that to time spent driving.
For a few people, any UV is a medical problem. Xeroderma pigmentosum (XP) is a rare inherited condition, affecting about 1 in a million people in the US and Europe, in which the skin can't repair UV damage. For people with XP and their families, UV-blocking film on car and home windows is part of daily life, not an upgrade.
How window film helps
- Almost all quality window films block 99% of UV, including clear films that barely change how the glass looks. The darkness of the tint doesn't decide UV protection; the film's UV inhibitors do.
- You don't need dark tint to be protected. Clear UV films are legal on the front side windows in most states, where dark tint often isn't. Check your state's tint law for the exact limits.
- Heat and glare too: films that also reject infrared keep the cabin cooler and cut the squinting on long drives.
Film doesn't replace sunscreen or sunglasses on long drives, but it takes the side windows from partial to near-complete UV protection.
What next
- Why tint your car: the full list of benefits.
- Types of window film: dyed, metal, carbon, ceramic and clear films compared.
- Compare real films and their specs in our window film brands and specs library.
Sources: Boxer Wachler BS, "Assessment of Levels of Ultraviolet A Light Protection in Automobile Windshields and Side Windows," JAMA Ophthalmology, 2016. Gordon JR, Brieva JC, "Unilateral Dermatoheliosis," New England Journal of Medicine, 2012. Butler ST, Fosko SW, "Increased prevalence of left-sided skin cancers," Journal of the American Academy of Dermatology, 2010. MedlinePlus Genetics, "Xeroderma pigmentosum."
