Car glass blocks most UVB rays, but lets through most UVA rays

The windshield of your car stops about 99% of ultraviolet B (UVB) radiation — the type that causes sunburn. Side windows and rear glass do the same. However, the same glass lets through roughly 50% to 63% of ultraviolet A (UVA) radiation, the type that penetrates deeper into skin and contributes to aging and skin cancer risk. This means you are not fully protected from UV damage during a drive, even though you feel safer inside the car.

The reason has to do with how glass is made. Standard automotive glass contains a chemical compound that naturally absorbs UVB wavelengths. UVA wavelengths are longer and pass through the glass more easily. Windshields offer better protection than side windows because they are angled and thicker, but neither blocks UVA completely.

The difference matters if you spend hours driving regularly. A commute of 30 minutes each way, five days a week, means you are exposed to UVA through the windows for roughly 2.5 hours weekly. Over months and years, that exposure adds up.

Key Takeaways

  • Windshields block about 99% of UVB rays but only 37% to 50% of UVA rays, leaving you partially exposed during long drives.
  • Side windows offer even less protection than windshields and let through more UVA radiation.
  • UVA rays penetrate glass and skin deeply, contributing to premature aging and skin cancer risk over time.
  • Window tint and UV-blocking film can reduce UVA transmission, though regulations limit how dark you can tint windshields in most places.

Why windshields and side windows protect differently

Windshields are laminated — two layers of glass bonded together with a plastic interlayer. That plastic layer absorbs UVB rays. The lamination also makes the windshield stronger and safer in a crash. Side windows and rear glass are usually tempered glass, a single layer treated with heat to make it stronger. Tempered glass does not have the UVB-blocking interlayer, so it offers less protection.

The angle of the windshield also matters. Because it is tilted, UVB rays hit it more directly and are absorbed more effectively. Side windows are vertical, so the angle of the sun changes throughout the day, and some rays pass through at angles where they are not fully blocked.

Neither type of glass was designed with UV protection as the main goal — that is a side effect of how the glass is manufactured. Windshields were laminated for safety, and the UVB blocking came along with that design.

UVA exposure during driving and skin damage

UVA rays cause two types of damage. They trigger the production of free radicals in skin cells, which breaks down collagen and elastin — the proteins that keep skin firm and elastic. This leads to wrinkles, age spots, and leathery texture over time. UVA rays also damage the DNA in skin cells, which can lead to melanoma and other skin cancers.

Because UVA rays pass through car glass, the left side of your face and arm (in countries where you drive on the right) can receive significant exposure during a long commute. Studies have found that people who drive for work often show more sun damage on the side of their face closest to the window. This is sometimes called "driver's side photoaging."

The damage is cumulative and does not require a sunburn. You can receive UVA exposure without feeling heat or seeing redness, which is why many people do not realize they are being exposed while driving.

How to reduce UVA exposure while driving

The most straightforward option is to explore a UV-blocking film to your windows. These films are transparent and do not significantly darken the glass, but they can block 99% of both UVA and UVB rays. You can have them professionally installed on side windows and rear glass. Most places have regulations about how dark you can tint a windshield — usually you cannot tint it at all, or only the top few inches — so check your local laws before installing film.

Another option is to wear sunscreen on your face and arms while driving, even on cloudy days. Sunscreen rated SPF 30 or higher blocks UVA and UVB rays. Reapply it every two hours if you are on a long drive, though this is less practical during actual driving than before you leave.

Lightweight long-sleeved clothing, a wide-brimmed hat, and UV-blocking sunglasses also reduce exposure. Some people use a sun shade on the windshield when the car is parked, which prevents the interior from heating up and also reduces UV exposure if you are sitting in a parked car.

Window tint regulations and what they mean for protection

Most states and provinces regulate how dark you can tint your windows. Windshields usually cannot be tinted at all, or only the top strip above the driver's line of sight can be tinted. Side windows and rear windows have limits that vary by location — some places allow 35% visible light transmission (meaning 65% is blocked), while others allow 50% or more.

These regulations exist for safety reasons: police need to see into vehicles during traffic stops, and drivers need to see out clearly. A darker tint blocks more light, including UV rays, but it also reduces visibility. UV-blocking film that is not tinted offers UV protection without reducing visibility or breaking the law, which is why it is a popular choice for people who want protection without the appearance of tint.

If you choose to tint your windows, check your local regulations before installation. A shop that installs tint can tell you what is legal in your area.

Frequently Asked Questions

Can I get skin cancer from driving with the windows down?

Yes. When windows are down, you have direct UV exposure with no glass protection at all. UVA and UVB rays reach your skin unfiltered. Wearing sunscreen and protective clothing is especially important on long drives with windows open.

Does tinted glass block more UV than regular glass?

Tinted glass blocks more visible light, which also blocks some UV rays, but the relationship is not direct. A dark tint might block 50% of UV rays, while a clear UV-blocking film blocks 99%. The tint color and darkness matter less than whether the glass has UV-blocking treatment.

What about windshield shades — do they work?

Windshield shades block UV rays when the car is parked, which prevents interior heat buildup and protects the dashboard from fading. They do not help while you are driving because you cannot see through them. Some people use them during work hours when the car is parked in the sun.

Is the UV exposure from driving enough to cause visible damage?

Over years, yes. People who drive for work often show more wrinkles and age spots on the side of their face closest to the window. The damage is gradual and may not be noticeable year to year, but it accumulates over a decade or more of regular driving.