Why do wrinkles appear? Here's the explanation.

NEW YORK (HealthDay News)—The fight to control wrinkles is a long one , with people using any number of lotions, creams and treatments to try to smooth their skin.

Researchers say they now know exactly why skin wrinkles .

“This is no longer just a theory,” said lead researcher Guy German , an associate professor of biomedical engineering at Binghamton University in upstate New York, in a press release. “We now have solid experimental evidence showing the physical mechanism behind aging.”

Laboratory experiments show that aged skin stretches, contracts, and bends under pressure, eventually forming wrinkles, according to findings published in the October issue of the Journal of the Mechanical Behavior of Biomedical Materials.

Essentially, wrinkles occur when a person's skin stretches in one direction and then contracts in the other , the researchers found.

The research team gave a hoodie as an example: after years of use, it will stretch in different places, just like that person's skin.

For the study, the researchers stretched small strips of skin from people aged 16 to 91 , simulating the natural forces at work on the skin every day. When skin stretches in one direction, it contracts in the other, the experts added.

But the contraction becomes greater with age, resulting in the formation of wrinkles.

“If you stretch Play-Doh, for example, it stretches horizontally, but it also shrinks in the other direction [and] becomes thinner. That's what skin does, too,” German said. “ As you age, that contraction gets bigger . And if your skin contracts too much, it buckles. That's how wrinkles form.”

This is exacerbated by age-related changes in collagen and elastin, proteins that provide structural support within a person's skin, the scientists added.

“Things degrade a little bit, and it turns out the skin stretches more laterally, which causes the actual wrinkles to form,” German added. “And the reason that happens in the first place is that your skin isn't stress-free. In fact, it stretches a little bit. So there are inherent forces within the skin itself, and those are the driving force behind wrinkles.”

Sun damage can also contribute to skin aging, Guy German noted. “If you spend your life working outdoors, you're more likely to have older, more wrinkled skin than office workers, for example,” German said.

“ Chronological aging and photoaging give you similar results. So go out and have a fabulous summer, but don't forget the tanning lotion—your future self will appreciate it.”