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Although the average level of UV rays blocked by front windshields surpasses 95 per cent, that level is much lower through the side as windows are not made of laminated safety glass.Maciej Bledowski/Getty Images/iStockphoto

Your car may be doing serious harm to your health. Slowly, inexorably – and especially if you live in sun-drenched climates. This belief is what drives Dr. Brian Boxer Wachler to chase the attention of automobile manufacturers and, hopefully, lead them to recognize what he considers a serious health issue.

Boxer Wachler's "a-ha" moment occurred while advising a patient on the proper sunglasses to wear to protect the eyes as much as possible – wraparound was the thinking. The patient, a woman in her 50s, with an eye condition called Keratoconus, mentioned that she had more age spots on the left side of her face than the right. Following along the same theme, Boxer Wachler realized he had been seeing a far higher incidence of cataracts in his patients' left eyes than their right eyes.

This triggered a thought: What if people had more sun damage on the left side of their faces because they were spending hours per day behind the wheel of a car – more pointedly, a left-hand drive car?

Armed with an Omega HHUVA1 meter that's used to measure UVA light, Boxer Wachler visited a number of car dealerships. But he wasn't kicking tires, he was taking measurements – of the UV protection offered by front windshields and side windows. He measured a range of vehicles and discovered that side windows were not offering the same level of UV protection as front windshields.

Taking into account all the different models the doctor tested, the average level of UV rays blocked by the front windshield was 96 per cent – a reassuring result. This quality is not by accident, it's a happy side effect: Windshields are made of laminated safety glass, which features a layer of polyvinyl butyral or ethylene-vinyl acetate sandwiched between two or more layers of glass. This design prevents the glass from shattering on impact. It also happens to block almost all of the sun's harmful rays.

In general, side windows are not made of laminated safety glass, although in some cars, such as the new Mercedes-Benz S550 and E550, they are. Most side windows, according to representatives from the manufacturer, use tempered safety glass. Boxer Wachler found that the side windows of the older vehicles measured offered an average level of protection of 71 per cent – in one, the level was only 44 per cent.

The car with the lowest score was a 2009 Mercedes-Benz E550, before this car featured laminated safety glass for side windows. The score for the side windows of a 2013 Mercedes-Benz S550 was 95 per cent, a shade below the 96-per-cent protection offered by the car's front windshield. A subsequent test by the doctor of various 2015 models from a range of manufacturers revealed similar average results. In this case, though, the lowest-scoring vehicles had side windows that blocked 60 per cent of UVA rays.

"I wasn't interested in attacking the car manufacturers for being irresponsible," Boxer Wachler says. "But I think the public perception is that, if you're in your car with the windows closed, you have a certain level of protection from the sun. This just may not be the case."

When reached for comment, representatives from Daimler AG noted that, in late 2014, they had an independent research firm study the issue of UV transmission in their car windows. The firm's findings correspond to those of the doctor.

Benz front windshields block at least 97 per cent of UV rays; tempered safety glass treated with a "privacy" tinting blocked about 90 per cent of UV rays; tempered safety glass with no tinting ("green glass") blocked between 70 and 75 per cent of UV rays. The manufacturer is reviewing whether to add additional UV protection to its windows made of tempered safety glass.

It also noted that there is an increased trend toward using laminated safety glass for all windows, but this movement is primarily because this glass also has better sound-deadening qualities.

Representatives from BMW acknowledged that they, too, were aware of the issue of UV protection offered by car windows. They recognized that tinting was an option offered in markets where privacy glass is allowed by law. "All of our SUVs offer standard 'privacy glazing' on side windows behind the B pillar (due to government regulations, not in front of B pillar)," a statement from BMW AG reads. "[This glazing] offers 100-per-cent UVB protection and UVA protection of 91 [to] 96 per cent." They went on to note the forthcoming 7 Series will offer a feature called "Climate Comfort Glazing," which provides 100 per cent UVA and UVB protection for all the windows.

General Motors, Honda and Toyota declined to comment on the issue, which has been on the radar for some time. A study released by the British Medical Journal in 1986 confirmed that solar keratosis and skin cancers were far more common on the right forearms and hands of Australian men and on the left side of Australian women's faces and necks.

At that time, the right-hand drive country had the highest rate of skin cancer in the world; the reasoning behind the results was that men drove more than women and sat higher in the seat, exposing their hands and arms; women sat lower, exposing their heads to the sunlight.

Another study, this one published in 2009 by the Journal of the American Academy of Dermatology, saw researchers at the St. Louis University School of Medicine examine more than 1,000 patients that were referred to a local skin cancer clinic. The results: People who spent the most time driving a car each week were more likely to develop skin cancers on the left side of their bodies and faces. In patients with malignant melanoma, the deadliest form of skin cancer, 74 per cent of tumours were found on the left side.

These findings are supported by Dr. Jennifer Beecker, national chair of the Sun Awareness Program of the Canadian Dermatology Association, who cited a further six studies that showed similar results. "It's been known for some time that car windows and windows in general don't offer enough protection from the sun's rays," she says. "In Canada, we're seeing huge increases in the number of people with skin cancers and other sun-related afflictions."

Research cited by Beecker indicates that the risk of melanoma in North Americans has skyrocketed – from one in 1,500 in the 1930s to approximately 1 in 50 today. In Canada last year, melanoma was the sixth-most prevalent type of new cancer cases in both men and women. Despite these statistics, Beecker acknowledges that the average person is not paying enough attention to sun protection, particularly when behind glass.

For his part, Boxer Wachler has some sage advice: "Take the guesswork out of whether cars have a high-level of UV protection by simply requesting a clear, non-tinted 100-per-cent blocking UV film on the side windows."

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