Long hours behind the wheel may increase the risk of skin cancer, according to a surprising new study. Facial skin cancers were found to occur more often on the left-side — the side that’s next to the window while driving — among a group of about 1,050 patients in Saint Louis. The findings were most significant for men.

While the results show only an association (not a cause-effect link) and would need to be replicated in a larger population to be viewed as firm, they call attention to what might be overlooked by otherwise sun-conscious citizens — exposure to UV rays through the car window.