On May 4, 2014, Dr. Brian Wachler was on a quest. Taking his daughter along to help, he visited several car lots in the Los Angeles area midday when UV radiation would be the greatest. Using a handheld Omega UV-A light meter, he determined how much harmful UV-A radiation was blocked by the front windshield and side windows of several makes and models of cars.
UV-A light is the longer wave portion of UV light that causes melanoma, eye cataracts, and other sun damage like wrinkles, sagging skin, age spots, and leathering of the skin. UV-B light is the shorter wave portion of UV light that causes sunburn. Thus, while both forms of UV light are harmful, the most harmful portion by far is UV-A.
Further, it should be noted that while skin cancer is often thought of as a relatively benign form of cancer, and maybe it is compared to pancreatic cancer or lung cancer, melanoma is by far the worst type of skin cancer to get. This is because melanoma (Stage IV melanoma) can spread through the lymph nodes to other parts of the body, most often the lungs, and is nearly always fatal when it does. In other words, skin cancer can kill you and should not be taken lightly. Preventing it is paramount!
So, what did Dr. Wachler and his daughter find?
They tested twenty-nine cars ranging in age from 1990 to 2014. Fifteen different automobile manufacturers were represented in the study.
There were several key findings:
1. Windshields Performed Much Better At Blocking UV-A Radiation Than Side Windows
Of the twenty-nine front windshields tested, they all performed relatively well, blocking between ninety-five and ninety-eight percent of all UV-A radiation. However, side windows only blocked an average of seventy-one percent of UV-A radiation, with the worst performing side windows only blocking forty-four percent of the UV-A radiation. While the top performing side window blocked ninety-six percentage of the UV-A radiation, you can see from the average that most side windows did not perform anywhere near this.
The dramatic difference in how much UV-A light front and side automobile windows block has to do with the difference in how they are manufactured. Car windshields are required by law to made from laminated glass so they won't shatter during an accident. Laminated glass consists of two panes of glass with a PVB (polyvinyl butyral) or EVA (ethylene-vinyl acetate) sheet of industrial plastic wedged between them to hold the little pieces of broken glass in place. It is this plastic layer that is most responsible for blocking UV-A radiation. On the other hand, side windows and other windows in cars are made of simple tempered glass. While it is stronger than "normal glass" like you have in your home windows, it lacks the inner plastic layer. Side windows may be specially coated to block UV-A light but many car side windows do not have this type of coating and most coatings are not as effective as the plastic layer in laminated glass.
2. Tinting On the Windows Did Not Seem To Matter
While you may think that your tinted windows are blocking the UV radiation, it is not! In fact, it is noteworthy that the various UV-A blocking coatings that are used on tempered side window glass are usually clear, not tinted. Many people ask, "Does glass tinting block UV light?" The answer is a resounding "NO!" Don't be fooled into thinking that you and your family are protected by tinted windows!
3. How Expensive the Car Was Did Not Seem To Matter.
You may be surprised to learn that the worst performing car in the study was a 2009 Mercedes E550. The side windows of this very expensive car only blocked forty-four percent of UV-A radiation! It was outperformed by a 2008 Honda Civic side window which blocked sixty-eight percent of UV-A radiation and an old 1990 Buick Riviera side window which blocked sixty-five percent of UV-A radiation. A 2004 Ford truck side window blocked seventy-six percent of the UV-A radiation.
So, we ask again, "Does car glass protect you from UV light?"
Answer: Not nearly enough! Further, side windows protect you very little in many cars.
Since the 1980s, American doctors have been aware that melanomas and cataracts occur more frequently on the LEFT SIDE of the body, due to intense UV radiation on the left side of the face, the left side of the neck, the left arm, and even the left scalp on people with thinning hair. However, the exact OPPOSITE trend is seen in countries like Australia and England where drivers sit on the opposite side of the car! Furthermore, studies have shown that melanomas and cataracts are more frequent in men, especially older men, who tend to drive more than women. However, this trend is changing as younger women are now driving more.
It is imperative that you protect yourself and your loved ones from UV-A exposure while driving or sitting in a car as a passenger! Unfortunately, many sunscreens do not block the UV-A portion of UV radiation. Further, they are messy to deal with and often contain harmful chemicals that get soaked into the skin.
Sun protective clothing like a sun shirt and wide brimmed sun hat are a MUCH better option for protection from the sun in the car. Look for sun protective clothing with a UPF 50+ rating to block more than ninety-eight percent of ALL UV radiation, including the most harmful UV-A radiation!
If you or your spouse or another loved one has a long commute, that UV-A radiation they are being exposed to every day on the left side of their body is CUMULATIVE. This means that every time they make that long commute, their risk of melanoma, cataracts, and other sun damage goes up a notch, i.e. there's no reset every day! On long road trips, when you have your kids in the back seat playing video games or "I spy," those side windows are not protecting them from the very harmful UV-A radiation. Luckily, it is much easier to get kids to put on a sun shirt than slather themselves in sunscreen! In fact, many kids find uv protection clothing for kids, including the "safari" style hats, fun to wear.
Keep in mind too that UV-A penetrates straight through clouds so you and your loved ones are at just as great a risk on cloudy days as bright sunny ones. You may want to keep an extra sun shirt and sun hat in the trunk of your car for any passengers and friends you may take with you on long trips.
Dr. Wachler's research was published in the July 2016 edition of JAMA Ophthalmology, a prestigious peer reviewed journal of the American Medical Association. All of the data they collected was tested more than once for accuracy so this is a robust study you can trust. You can see a chart showing all percentages of UV-A blockage for every car tested in his paper.