In North America, cataracts and skin cancers appear on the left side of the face at a greater frequency than on the right. Because the opposite correlation occurs in countries that drive on the other side of the road, experts have long suspected that sun exposure through the driver-side window contributes to the accumulated ultraviolet (UV) radiation exposure that exacerbates the formation of cataracts and certain skin cancers.

A recent study, published in JAMA Ophthalmology, assessed the levels of UV-A light that seeped through the front windshield and driver-side window of several automobiles.

People who are darker pigmented are not as photosensitive to glare as those with fair skin and light eyes, but they should still reach for their full spectrum UV shades when facing the sun.