A startling photo published in the New England Journal of Medicine shows the long-term effects of sun exposure, but only on one side of the face.
Sixty-nine-year-old delivery-truck driver Bill McElligott spent 28 years with the left side of his face exposed to the sun. Subsequently, while the right side of his face is aging quite well, the left side looks considerably older than the right.
Dr. Jennifer R.S. Gordon, the doctor who treated the patient, tells the Toronto Star that she'd "never seen sun damage that one-sided," adding, "Sideways, he looks like two different people."
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McElligott, who started using sunscreen three years ago, is set to undergo laser resurfacing on his left side.
While he shows no signs of skin cancer — his milk-truck windows blocked the cancer-causing UVB rays — he is still at high risk, Gordon warns:
"Skin cancer is usually the result of 20 to 30 years accumulation. Lots of people his age are starting to develop it."
Ultraviolet A (UVA) light from the sun, which can cause deep damage in the skin, can easily penetrate window glass and even light clothing, Gordon tells LiveScience.
"We think its because it (UVA) can penetrate more deeply into the skin than UVB and affect your collagen and elasticity," Gordon tells ABC News. "When you destroy those, that's what gives you the aging appearance that we see."
McElligott first sought treatment three ago for his uneven sun damage — called "unilateral dermatoheliosis" — after his grandchildren started asking about his two-faced appearance.
"Only reason I went in, the kids were asking me what these bumps are and it's hard to explain to little kids, so I went to see if I could have those bumps removed," he tells ABC News.
The moral of this story? Wear sunscreen.
Which brand is best? "The one you will use," Gordon says. Find a water-resistant sunscreen with a consistency you like — and wear it daily.
Here are 10 sunscreens to beat the heat.
Watch the video below about how tanning salons in Canada are allowing underage tanning.