Ultraviolet (UV) radiation is electromagnetic energy from the sun, categorized into two main types: UVA and UVB. UVA rays have a longer wavelength, penetrating deep into the skin and contributing to aging and long-term damage. UVB rays have a shorter wavelength and are the primary cause of sunburn. UV rays do penetrate car windows, but the level of protection varies significantly depending on the type of glass used. Certain parts of a vehicle’s glass allow a substantial amount of harmful UV radiation to pass through, creating an often-overlooked source of sun exposure.
How Different Types of Car Glass Block UV Rays
The level of UV protection is determined by the type of glass used, primarily laminated or tempered safety glass. Windshields are nearly always constructed from laminated glass, consisting of two layers of glass with a polyvinyl butyral (PVB) plastic layer sandwiched between them. This PVB interlayer is highly effective at blocking UV rays, typically filtering out approximately 98% or more of both UVA and UVB radiation. While laminated construction is primarily for safety, the PVB layer provides the added benefit of superior UV defense.
The side and rear windows of most vehicles are made from tempered glass. This glass is manufactured through a rapid heating and cooling process to increase strength and ensure it breaks into small, dull fragments upon impact. This process does not inherently include a UV-blocking agent like the PVB interlayer. Tempered glass effectively blocks almost all UVB rays, but it is far less effective against the deeper-penetrating UVA rays.
Studies show that while an average windshield blocks around 96% of UVA rays, the typical side window made of tempered glass may block only about 71% of UVA. This difference exposes passengers to a significant amount of UVA radiation through the side windows, even when closed. Therefore, the location in the car dictates the level of protection. Front seat occupants are shielded by the laminated windshield but remain vulnerable through the side glass.
The Consequences of Chronic UVA Exposure While Driving
The long-term penetration of UVA rays through side windows poses a health concern for frequent drivers and commuters. UVA radiation travels deep into the skin, damaging collagen and elastin fibers, which leads to photoaging. This chronic exposure accelerates the appearance of wrinkles, sagging, and brown spots on the skin.
Dermatological research documents “driver-side syndrome,” where frequent drivers exhibit higher rates of sun damage and skin cancers on the side facing the window. For drivers in countries like the US, this often means a greater incidence of skin cancers on the left arm, hands, and face. Skin cancer risk is elevated because UVA rays cause genetic damage that accumulates over time, even at lower doses.
The deep penetration of UVA means this exposure is insidious because it does not result in an immediate sunburn. This lack of immediate sensation causes many drivers to underestimate the cumulative damage occurring during commutes or road trips. The resulting damage includes a significantly higher likelihood of developing all types of skin cancers on the chronically exposed side, not just cosmetic issues.
Reducing UV Exposure Inside Your Vehicle
Drivers can take several effective steps to mitigate the risk of chronic UVA exposure. One effective solution is applying specialized aftermarket window films, often called window tinting, to the side and rear windows. High-quality films, particularly ceramic or metallic formulations, are engineered to block up to 99% of all UV rays, including the UVA that passes through tempered glass.
When considering window films, drivers must check local and state regulations regarding the allowed Visible Light Transmission (VLT) for side windows, as laws vary. Even clear or very light-colored films can be highly effective at blocking UV radiation, meaning a dark tint is not required for maximum protection. Professional installation ensures the film is correctly applied and provides the advertised level of UV defense.
Personal Protection Habits
For personal protection, drivers should adopt habits that supplement the vehicle’s glass protection. Applying a broad-spectrum sunscreen with a minimum Sun Protection Factor (SPF) of 30 to all exposed skin, especially the hands and arms, is a simple measure. Wearing UV-protective clothing, such as lightweight long-sleeved shirts, and using sunglasses that offer 100% UV protection, can further shield the skin and eyes.