Windshield and UV exposure

Windshield and UV exposure

As the summer draws to a close and I have finished my 20th road trip with my three children who frequently complain of “being too hot” or that the “sun is in my eyes” while in the car, I would like to raise attention to the need for sun protection for all passengers in cars. Sun protection in the car is almost always neglected, particularly for passengers. As thoughtful parents, we lather our kids with sunscreen before going to the pool or beach, but do we really remember to do this, or to provide sunglasses before embarking on a 5-hour car ride? Many people do not. We must raise awareness of the risk of UV light in cars, and take better care of both our children and ourselves.

Windshield glass is federally regulated to allow in a maximum amount of light for visibility, but has no requirements for sun protection. Many people do not understand the difference between UVA and UVB protection, let alone that UVB radiation is blocked by the window glass, but UVA radiation is not, and reaches the skin and eyes through glass. By law, windshields must be made of laminated glass, which includes two 2.1-mm layers of glass separated by a 0.8-mm piece of plastic. The glass is made to break easily upon impact and the plastic then stretches to absorb the impact. The thin layer of plastic also helps windshields absorb nearly all of the sun’s UVA and UVB rays. Sunroofs also contain UV-protective technology, which blocks UVA and UVB radiation while also keeping the car cool and protecting against direct sun exposure. However, rear windows do not offer the same protection.

Side and rear windows are made of a cheaper tempered glass that does not include a plastic layer, thereby offering no UVA protection. In a study by Butler et al. reviewing 900 head and neck cancers, 53% were found on the left side, and those who spent more hours driving each week had a higher chance of getting a left-side skin cancer (J Am Acad Dermatol. 2010 Dec;63[6]:1006-10). Many automakers have not helped this problem; while there is higher-SPF glass that can be used, it is more costly for automobile manufacturers – and ultimately for consumers. A cheaper and more practical alternative is a UV film that can be applied to the glass; these films both improve UV protection and cool the car. In addition to providing sun protection, it can be assumed that the subsequent reduction of temperature within a car decreases the usage of air conditioners, thus improving both fuel economy and the environment.

Aftermarket window tinting and UV films can also be applied by glass-tinting companies and auto dealers for $150-$200. Companies like Solar Gard, LLUMAr, and 3M offer window films that can block UV rays. While these are available, the legal allowable tint limit varies from state to state. Visible light transmission (VLT) is the measurement of the percent of visible light that gets through a car’s window. The lower the VLT, the darker the tint. Most states prohibit less than 50% VLT for the driver and front passenger window, and 35% for the rear passenger, side, and rear windows.

To mitigate this, I offer patients with severe photo-dermitides a letter of medical necessity to the DMV to allow a higher percentage of tinting and recommend that they get aftermarket UV-protective films or tints on their vehicles. Regardless of whether higher tints are an option for them, sun protection of the skin and eyes is recommended for all passengers. Sunscreen with broad-spectrum coverage is recommended regardless of how long a car ride might be, and it is recommended that individuals keep the sunroof closed while driving for added UV protection. The use of polarized sunglasses for adults and children is also recommended to avoid UV damage to the eyes. Sunscreens and glasses with protection against blue light are also recommended for passengers who stare at screens and tablets during long car rides.

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