Car windows block most UVA rays, but not all of them

Standard car windows stop about 99 percent of UVB rays — the ones that cause sunburn — but they let through roughly 50 to 70 percent of UVA rays. This matters because UVA rays penetrate deeper into skin and contribute to premature aging and skin cancer risk, even on cloudy days and even through glass.

The difference comes down to how glass is made. Car manufacturers add a coating to the windshield that blocks most ultraviolet light, but the side and rear windows are usually plain glass. Plain glass naturally blocks UVB but is nearly transparent to UVA. That means your left arm and face get UVA exposure during a long drive, even though you are not getting sunburned.

The amount of UVA that reaches you also depends on the angle of the sun, the time of day, and how old your windows are. Older glass may have yellowed or degraded, which can change how much UV passes through.

Key Takeaways

  • Windshields block about 99 percent of UVB rays but only 30 to 50 percent of UVA rays.
  • Side windows and rear windows are plain glass and block almost no UVA, letting through 50 to 70 percent.
  • UVA exposure through car windows contributes to skin aging and skin cancer risk over time, even though you will not sunburn.
  • Window tint and UV-blocking film can reduce UVA transmission, though tint darkness is regulated by state law for front windows.

Why windshields and side windows are different

Your windshield has a laminated construction — two layers of glass bonded with a plastic interlayer — and that interlayer is treated to absorb UV light. This design protects you from flying debris in a crash and happens to block most ultraviolet radiation. Manufacturers have been adding UV protection to windshields since the 1980s.

Side windows and rear windows are typically single-pane tempered glass with no UV-blocking treatment. Tempered glass is stronger than regular glass and shatters into small, less dangerous pieces in a crash, but it does nothing to stop UV rays. The glass itself is transparent to UVA, so the rays pass straight through.

This is why dermatologists often see sun damage on the left side of the face and neck in people who drive regularly — the side window exposure adds up over years and decades.

How much UVA actually gets through

The exact amount of UVA transmission varies by car model, glass manufacturer, and whether the glass has any tint. Laboratory testing shows that untinted side windows typically transmit 50 to 70 percent of UVA rays. Windshields transmit roughly 30 to 50 percent, depending on the specific laminate and interlayer used.

This means that during a two-hour drive with the sun on your left side, you are receiving a meaningful dose of UVA even though the glass is keeping you from burning. The cumulative effect over months and years is what increases skin cancer risk and causes visible aging.

Tinted windows reduce UVA transmission further. A light tint (around 20 percent visible light transmission) can cut UVA by 40 to 60 percent compared to untinted glass. Darker tint blocks more, but front window tint is restricted by state law in most places — usually to 28 to 35 percent visible light transmission — for safety and law enforcement reasons.

What window tint and UV film can do

If you want to reduce UVA exposure while driving, you have two main options: aftermarket window tint and UV-blocking film.

Window tint is a thin, colored film applied to the inside of the glass. It blocks both visible light and UV rays. The darkness is measured as visible light transmission (VLT) — the percentage of visible light that passes through. A 50 percent VLT tint blocks half the visible light and significantly more UV. Tint is permanent and lasts the life of the window, though it can bubble or peel over time if applied poorly.

UV-blocking film is a clear or lightly tinted film designed specifically to block ultraviolet rays while letting most visible light through. It does not darken the window noticeably, so it does not run into state legal limits for front windows. UV film is also permanent but can be removed if you sell the car.

Both options require professional installation for best results. Tint is cheaper (typically $150 to $400 for a full car) but changes the appearance of your windows. UV film costs more ($300 to $800) but is invisible and does not affect visibility.

State laws on window tint

Most states allow tint on rear and side windows but restrict how dark tint can be on the front side windows and windshield. Front side window limits typically range from 28 to 50 percent VLT, depending on the state. Some states have no restrictions on rear windows.

A few states do not allow any tint on front windows at all. Before you have tint installed, check your state's specific rules — a shop that installs illegal tint can result in a traffic citation and a requirement to remove it.

UV-blocking clear film is legal everywhere because it does not reduce visible light transmission and does not interfere with law enforcement visibility.

Other ways to reduce UVA exposure while driving

If tinting is not an option or you prefer not to modify your windows, you can still reduce UVA exposure during drives. Sunscreen rated SPF 30 or higher, applied to your face, neck, and arms before driving, blocks 97 percent of UVB and most UVA (look for "broad-spectrum" on the label). Reapply every two hours if you are on a long drive.

A wide-brimmed hat or a sun visor clipped to your visor blocks direct rays from hitting your face. Long sleeves or UV-protective clothing (labeled UPF 50+) cover your arms. Sunglasses that block 100 percent of UVA and UVB protect your eyes and the delicate skin around them.

Parking in shade or in a garage when you are not driving prevents glass exposure when the car is stationary. If you park in the sun regularly, the interior of your car also heats up, which can damage the dashboard and interior materials over time.

Frequently Asked Questions

Does my windshield protect me from skin cancer?

Your windshield blocks most UVB rays, which cause sunburn, but lets through 30 to 50 percent of UVA rays. UVA contributes to skin cancer and aging. So while the windshield offers some protection, it is not complete. Using sunscreen and other sun protection during long drives is still important.

Can I get a tan through car windows?

You can get a very slow tan through car windows because UVA rays pass through, and UVA is involved in tanning. However, the process is much slower than direct sun exposure because the glass blocks a significant portion of the rays. You are more likely to see skin damage and aging than a noticeable tan.

Does window tint fade over time?

Quality window tint can last 5 to 10 years, though cheaper tint may fade or bubble sooner. Fading happens because UV rays gradually break down the dye in the film. UV-blocking clear film lasts longer because it has no dye to fade, though it can eventually yellow slightly.

Is UV-blocking film worth the cost?

If you drive regularly and want to reduce skin cancer and aging risk without darkening your windows or running into legal limits, UV film is worth considering. The cost ($300 to $800) is a one-time expense that lasts the life of the window. Sunscreen is cheaper but requires reapplication every two hours.

Do tinted windows keep the car cooler?

Yes. Tinted windows reduce the amount of solar heat entering the car, which can lower interior temperature by 10 to 15 degrees on a hot day. This also reduces the load on your air conditioning system and can slightly improve fuel economy. UV-blocking clear film provides some cooling benefit but less than visible tint.