It's easy to assume that once you're inside a car, you're out of the sun. The windows are closed, the air conditioning is on, and there's a layer of glass between you and the sky. But that glass does not protect you as much as it looks like it should — especially on the side you're sitting on.
Why This Matters
There are two types of UV radiation that reach your skin: UVB, which causes sunburn, and UVA, which penetrates more deeply and drives skin aging and long-term skin cancer risk. Most window glass is reasonably good at blocking UVB. UVA is the problem.
The reason comes down to the type of glass. Front windshields are made of laminated glass — two layers of glass bonded with a plastic interlayer that happens to block most UVA along with UVB. Side windows, rear windows, and sunroofs are typically made of tempered glass, which blocks UVB but does little to stop UVA from passing through.
Over time, that gap shows up on skin. The Skin Cancer Foundation points to a case published in the New England Journal of Medicine: a truck driver who spent 28 years behind the wheel developed visibly aged, wrinkled, sun-damaged skin on the side of his face nearest the window, while the opposite side stayed comparatively smooth. In the United States, where drivers sit on the left, melanoma and non-melanoma skin cancers are reported more often on the left side — consistent with which side gets more direct sun through the glass. In countries where drivers sit on the right, such as Australia and the UK, the same pattern would be expected to show up on the right side instead. The side isn't the point — steady, one-sided UVA exposure over years is.
This adds up fastest for people who spend a lot of time driving: daily commuters, road-trippers, delivery and rideshare drivers, and anyone who treats a long car ride as "indoor" time that doesn't need sun protection.
What to Do About It
You don't need to avoid driving — you need to treat the side window the way you'd treat any other unprotected UV exposure.
- Apply broad-spectrum sunscreen to your face, hands, and arms before longer drives — the same way you would for time outdoors.
- Wear UPF-rated clothing or long sleeves on the arm closest to the window, especially on regular commutes.
- Wear UV-blocking sunglasses to protect your eyes, since side windows won't stop UVA from reaching them either.
- Consider UV window film for your side windows and sunroof — the Skin Cancer Foundation notes it can block over 99% of UVA and UVB when properly installed. This matters most for older or high-mileage vehicles, where factory glass protection tends to be weaker.
- If you drive frequently for work, build in regular skin self-exams and mention your driving time to your dermatologist.
Key Takeaway
Your windshield is doing its job, and newer side windows do it better than they used to. But "better" isn't "solved" — most side windows still let meaningfully more UVA through than windshields, especially in older or high-mileage vehicles, and that adds up over years of driving.
UVTREK reminder: if the sun's coming through the glass, it's still reaching your skin.
Boxer Wachler, B.S. (2016): "Assessment of Levels of Ultraviolet A Light Protection in Automobile Windshields and Side Windows," JAMA Ophthalmology — 29 vehicles tested; windshields blocked 96% of UVA on average (range 95–98%), side windows blocked 71% on average (range 44–96%).
Axelson, G.E. et al. (2025): "Evaluation of UV-A and UV-B Transmission Through the Windows of Gas, Hybrid, and Electric Vehicles," Archives of Dermatological Research, vol. 317 — 34 vehicles tested (2015–2025 model years); windshields blocked 99.25% of UVA on average, side windows blocked 88.78% on average; vehicle mileage predicted protection better than model year.
The Skin Cancer Foundation: UV Window Film & Tint guidance, including the NEJM truck-driver case and window film UV-blocking performance.
University of Utah Health: "Car Windows Won't Protect You From UV Rays," sun protection guidance for drivers.