Hyaluronic acid is a natural sugar that binds water molecules together to keep your skin plump and hydrated. It is also the "jelly" in your eyeball as well as a lubricant in your joints. The popular wrinkle fillers Juvéderm and Restylane use synthetic hyaluronic acid as an active ingredient. Aside from connective tissue and hyaluronic acid, the dermis is also where you'll find the sebaceous glands (or oil glands)— concentrated primarily on your face, chest, back, and scalp— that secrete sebum (oil), your body's natural moisturizer. Sebum is what keeps your skin soft, supple, and waterproof. (After all, you won't melt if you walk in the rain or take a dip in the ocean, right?) Too much oil, however, can make your skin shiny and your makeup smear.
There are a number of reasons for why the sebaceous glands might go into overdrive, including stress, hormonal fluctuations associated with puberty and your menstrual cycle, and even certain foods. Overactive glands pump out lots and lots of oil, causing the pores to enlarge (which is why people with oily skin tend to have bigger pores). Excess oil on the scalp can make your hair feel greasy as well as predispose you to yeast overgrowth and dandruff . But choose the right foods, and you can modulate your skin's sebum production and control such conditions as acne and dandruff.
Did You Know . . .
When you get inked, tattoo pigment is injected past the top layers of the skin and deep into the dermis. Since this part of the skin is constantly being patrolled for "invaders," and tattoo ink is technically a foreign substance (biologically speaking, it's not really supposed to be there), immune cells called macrophages attempt to gobble it up and digest it. That's why tattoos fade over time.
Skin Enemy #3: Free Radicals
You've heard about them before in countless skin-care ads and magazine articles, but what the hell are free radicals and why should we care about them? Without getting too technical (for those of you who aren't science nerds), free radicals are atoms or molecules with an unpaired electron in their outermost shell. Th is makes them highly unstable and prone to undergo spontaneous chemical reactions in the hope of "stealing" an extra electron from a neighboring molecule.
Let's try an analogy: A free radical is not unlike a car with three wheels— you need the fourth to drive in a straight line and to stop you from wobbling and veering off course. But if you steal a tire from someone else's car, now they're left with an unstable ride. Likewise, when a free radical steals an electron from, say, a collagen or DNA molecule, those cells no longer function as intended, and that can have serious consequences. For example, it's believed that some forms of cancer are caused by chemical reactions between free radicals and DNA. According to the "free radical theory of aging," longterm free radical damage is the cause of most age- related diseases, including arthritis, Alzheimer's, and atherosclerosis. And in the skin, free radical damage causes a breakdown of collagen and elastin, leading to wrinkles, sagging, and discoloration. Put simply, free radicals are the reason that our bodies start to break down over time.