Summer is upon us, which means more of the country is driving with the window down, elbow resting on the door.

If that sounds like you, consider limiting your open air driving to an open sunroof, and only if you wear a hat. That's because a new study shows a link between driving and the incidence of skin cancer on the left sides of people who drive a lot -- the side exposed to the sun.

Researchers at the University of Washington in Seattle have found that Americans have a tendency to develop the worst forms of skin cancer – notably melanomas and merkel cell carcinomas – on the left side of their bodies. There is an especially high incidence of cancers discovered on the upper arm, according to a study published in The Journal of the American Academy of Dermatology.

This report adds to a growing body of evidence that driving can increase a motorist's exposure to ultra-violet (UV) light, which is linked to skin cancer. In countries like the U.S., where drivers sit on the left side of their car, studies have found more cancers form on the left side. Other research, including a 1986 report from Australia, found that in countries where the steering wheel is situated on the other side of the vehicle, there are more cancers and pre-cancerous growths on the right side of a driver.

That's pretty compelling evidence that driving has a big impact on incidence of skin cancer.

The incidence of cancer is most severe, suggest the authors of the new University of Washington study, for people who drive with a window open, drive convertibles, or those who simply spend an extensive amount of time behind the wheel; those, for example, who make their living driving.

The solution is rather simple. Auto glass today filters out most of the bad UV that can cause skin cancer, so driving with windows up and the air conditioner on is a better choice, even though your fuel economy will be worse. Too, side glass does not have quite as much UV blocking material as windshields.

A layer of glass tinting applied by an after-market detailing shop is one answer, especially for those who drive for a living and are in a vehicle all day long. Long sleeve shirts for those drivers is also an obvious choice, though warm summer days seem to beg for short sleeves. On those days, sunscreen on your arm, neck, face and head is advised.

Most people would not think of applying sun screen if they intend to be in the car all day. But a bit of prevention could be worth a lot of cure.