The risk of getting burnt through a car window is a common concern for drivers and passengers. While a “burn” is usually associated with immediate heat, the actual risk comes from invisible ultraviolet (UV) radiation, which causes sunburn. Understanding how different types of automotive glass interact with these rays reveals significant differences in protection depending on where you are sitting.
The Science of UV Radiation and Glass
Solar ultraviolet radiation is categorized into two main types that reach the Earth’s surface: ultraviolet A (UVA) and ultraviolet B (UVB). Their wavelengths determine how deeply they penetrate the skin and the damage they cause. UVB rays have a shorter wavelength and are primarily responsible for causing sunburn and blistering.
UVA rays have a longer wavelength, allowing them to penetrate deeper into the skin’s layers. These rays contribute significantly to premature skin aging, wrinkles, and deep cellular damage, and they are strongly linked to skin cancer development. Standard, untreated glass naturally blocks almost all shorter-wavelength UVB radiation. However, the longer-wavelength UVA rays pass through ordinary glass much more readily, creating an exposure risk even when indoors.
Why Windshields Offer Superior Protection
The high level of UV protection offered by the front windshield results from specific engineering required by safety regulations. Windshields use laminated glass, consisting of two sheets of glass bonded together by a transparent layer called polyvinyl butyral (PVB). This PVB interlayer is designed to prevent the glass from shattering upon impact, a safety requirement that also provides sun protection.
The plastic PVB layer is highly effective at absorbing UV light. This laminated construction blocks virtually all UVB radiation and filters out an estimated 94% to 98% of UVA rays. This protection level is comparable to a broad-spectrum sunscreen with an SPF of 50 or higher. Consequently, the risk of UV damage through the front windshield is low for both the driver and the front passenger.
The Risk Posed by Side and Rear Windows
The side and rear windows of most cars utilize tempered glass, a single layer treated for strength. Tempered glass is designed to crumble into small, blunt fragments if it breaks, but it lacks the protective PVB interlayer. While this glass effectively blocks UVB rays, it allows a significant portion of the longer-wavelength UVA rays to pass through.
Studies show that car side windows may only block about 65% to 71% of UVA radiation, allowing nearly one-third of the penetrating rays to reach occupants. For frequent drivers, this persistent exposure leads to accumulated skin damage on one side of the body. Research has identified an increased prevalence of skin aging and skin cancer, including melanoma, on the left side of the face and arm for drivers in left-hand drive countries. The risk stems from chronic, low-level exposure to UVA rays over years of commuting, not from a sudden sunburn.
Enhancing Your Vehicle’s UV Defense
Since standard side windows do not provide comprehensive UV protection, drivers can reduce their long-term exposure. One effective method is applying a clear or tinted UV-specific window film to the side and rear windows. High-quality aftermarket films can block over 99% of all UV radiation, offering complete protection without darkening the glass. Before installation, drivers must ensure that any window tinting adheres to local legal restrictions regarding visible light transmission.
Simple personal measures also provide immediate defense against penetrating UVA rays while driving. Wearing protective clothing, such as long-sleeved shirts, sun-protective gloves, and wide-brimmed hats, covers the most vulnerable areas. Applying a broad-spectrum sunscreen with an SPF of 30 or higher to exposed skin, particularly the hands, arms, and face, is a practical habit for anyone spending long periods in a car.