Identical twins -- they come from around the country once a year to attend a festival of twins in Twinsburg, Ohio, just outside Cleveland.
"We can compare the twins that have different social behaviors ... and see how those factors make a difference in their appearance," said Dr. Bahman Guyuron of University Hospital, Case Medical Center. Guyuron is the author of the study comparing 186 pairs of twins.
Many times there is a glaring difference reflected in the photos of twins. When comparing a pair of twin sisters, one who smokes and one who doesn't, for instance, the smoker has tiny, telltale vertical lines around her lips and longer, deeper wrinkles around her eyes.
"That's because smoking shrinks tiny blood vessels in the face so the skin is not being nourished," said Dr. Darrick Antell of St. Luke's Roosevelt Hospital and the author of one of the first twin studies. "Smoking dehydrates the skin so it's much drier."
There's also aging from excessive sun exposure. Twin sisters Gaye and Gwynn Verbit are now 72 years old. Gaye lives in Hawaii and worshiped the sun, eager for a tan. Her sister Gwynn lives in Baltimore, Md. and avoided the sun. The result? Gaye's skin today is coarser with much deeper creases around her cheeks and eyes.
"I knew about the risks but I didn't care," Gaye said. "It was the 70s and I was just more interested in having a good time."
The study even documents aging from divorce and the subtle toll stress has on the skin. Stress can lead to added lines beside the mouth and darker skin under the eyes.
Researchers have known that specific behaviors can be harmful to the skin, but until they studied twins, they never realized just how much.
The good news is, by changing lifestyles, "the damage can be stopped and also some of the damage reversed. Because our bodies have a tendency to rejuvenate," said Guyuron.
Adopting healthier lifestyles to slow the signs of aging.