WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to why@mentalfloss.com.

Our skin is supposed to stretch. We do it every day when we squint in the sunlight, make a silly face, smile, laugh, pout, or furrow our eyebrows. Each time our skin stretches, tiny lines and grooves start to form below the surface. Over time, the outside skin gets thinner and dryer, and it falls deeper into those little grooves. As we get older, we also lose some of the stuff in our skin that helps it to stretch and then return to its normal place. 

First, let’s talk about our three layers of skin. The outside part is called the epidermis (eh-pih-DER-mis). That’s the part you can see. Under that is our dermis, where we have stretchy fibers called elastin that let our skin stretch and then go back to its normal position, just like an elastic hair band. The dermis layer also has collagen (KAHL-uh-jen), a protein that helps it stay sturdy and grow new skin cells. Under the dermis is the deep subcutaneous (sub-kyoo-TAY-nee-us) layer, which stores fat. As we get older, we start to lose collagen, elastin, fat, and oils made by our skin that keep it moisturized, or less dry.

There are lots of reasons. Our bodies make less of these things as we age, so our skin gets thinner, drier, and less stretchy. The Sun’s ultraviolet (UV) light also breaks down collagen and elastin fibers. This causes more lines and wrinkles. But wrinkles are just a part of life. One day, you’ll have them too. Take good care of your skin by wearing sunscreen and drinking plenty of water to help your skin stay moisturized.

For further reading, visit Kids Health.