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HOW COME? Wrinkles are just a side effect of being human

Why does your skin wrinkle as you get older? asks Christopher McKnight, of Kings Park, NY.

Wrinkles and lines on our skin are a side effect of being human. Covered in mostly hairless, unprotected skin, we live on the surface of a planet, its sun shining bright -- while meanwhile socializing with other humans and animals, our facial expressions constantly changing as we do.

Lines are most visible on our face. Unlike skin on the rest of the body (like the legs), facial skin is attached to the muscles underneath. That makes it possible for us to smile, frown, and look surprised or perplexed -- over and over.

Meanwhile, Earth's gravity is always tugging on us, year after year, pulling our skin downward. But it's ultraviolet radiation from our home star that does the most damage. High-energy UV rays penetrate into the dermis, the skin's inner layer, damaging its network of collagen and elastin fibers. The skin loses some of its support structure, holds less water, and thins, becoming less elastic. And, like paper, skin that is drier, thinner and stiffer also folds more easily, its repeated creasing leaving visible traces.

But everyone's skin ages differently. Some people develop very few wrinkles, and that may be partly due to genes. Naturally dark skin is less prone to wrinkling, since the more melanin pigment in skin, the harder it is for UV rays to penetrate. The darkest skin shades, researchers say, are equivalent to a built-in SPF 13 sunscreen.

When we're very young, our skin springs smoothly back into place when we stop frowning. But as we get older, the small creases that appear between our brows become visible all the time, and slowly deepen. (Skin on the rest of the body changes, too. Just compare the sun-exposed skin on your hands and arms to skin that has stayed under wraps.)

As for the face, we could do an experiment, leaving one half protected from sunlight, the other half exposed, observing the changes over time. Few might be willing to sign up. But people who drive for a living, like long-haul truckers, may be conducting their own experiment.

A 2012 report in the New England Journal of Medicine showed the changes in the skin on opposite sides of a trucker's face. UV-A light penetrates skin more deeply than the UV-B form -- and it also zips through glass. The left half of the driver's face was exposed for decades to sunlight streaming through the side window. The result? Significantly more wrinkling and loss of elasticity, and skin that was damaged in myriad ways.

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