Aging skin stretches, contracts and buckles under pressure - and that's how wrinkles form, according to new experimental evidence from scientists at Binghamton University, State University of New York.
Examining human skin samples, a research team including Binghamton University Associate Professor of Biomedical Engineering Guy German found that older skin is more prone to wrinkles. Why? Wrinkles form when your skin stretches in one direction and contracts in the other direction, causing it to buckle - and this gets more pronounced as you age.
Consider your favorite hoodie, for example. After years of wear, it gets stretched out in different places. Your skin does something similar.
"This is no longer just a theory," said German. "We now have hard experimental evidence showing the physical mechanism behind aging."
Scientists have long believed that skin wrinkles as you age due to a number of factors (e.g., genetics, pathological conditions and solar photodamage. Previous research using computational models has shown changes in the mechanical properties and structure of the dermal layer (the skin layer that contains collagen and elastin and provides structural support) that come with aging, but this has never been validated experimentally, with actual skin samples, until now.
This research is one of German's lifetime goals, a "Holy Grail" in skin mechanics, he said. The cosmetics industry releases so many different anti-aging products, it can be headache-inducing to know what is good and what is snake oil.
"When I got into this field, that was one of my goals - can I figure out aging?" said German. "Because if I look at the TV, the radio, online, at shops, I'm being told 1,000 different things about how to improve my skin health, and I want to know what's right and what isn't. And so I thought I'd skip to the end and try and figure it out myself. "
German and former Binghamton graduate student Abraham Ittycheri and undergraduate student Alejandro Wiltshire used a low-force tensometer to stretch tiny strips of skin from people ages 16 through 91, simulating the forces the skin naturally experiences. They found that when skin is stretched in one direction, it contracts in the other direction. But this contraction gets bigger with age, resulting in the formation of wrinkles.
"If you stretch Silly Putty for instance, it stretches horizontally, but it also shrinks in the other direction - it gets thinner. That's what skin does as well," said German. "As you get older, that contraction gets bigger. And if your skin is contracted too much, it buckles. That's how wrinkles form."
Your skin has one set of mechanical properties when you're young, but as you get older, things begin to change and get a bit "wonky," said German.
"Things degrade a bit, and it turns out the skin stretches laterally more, which causes the actual wrinkles that form," said German. "And the reason why that exists in the first place is that your skin is not in a stress-free state. It's actually stretched a little bit. So there are inherent forces within your skin itself, and those are the driving force towards wrinkles."
With summer approaching, German noted that premature aging from spending chronic periods out in the sun can have the same effect on your skin as chronological aging.
"If you spend your life working outside, you're more likely to have more aged and wrinkled skin than those who are office workers, for example," he said. "Chronological aging and photoaging give you similar results. So go and have a fab summer, but don't forget the suntan lotion - your future self will appreciate it."
The paper, "Elucidating the Mechanistic Process of Age Induced Human Skin Wrinkling," was published in the Journal of the Mechanical Behavior of Biomedical Materials.
