You probably expect to get some wrinkles on your skin as you age, especially on your face. Crow's feet and laugh lines around the eyes and cheekbones are particularly common, but other areas are also prone to wrinkling. Your lips are no exception. Although they aren't likely to look like prunes, your lips aren't immune to the aging process. As you get older, lips tend to thin and lose their fullness.

If you're not quite ready to lose your lips' plumpness, you might want to consider a filler. Many of the wrinkle fillers that attempt to fix marionette lines or crow's feet can work to fill out lips as well. If you're thinking of getting lip-filler injections, be sure to discuss your options with your doctor; some fillers, including those that contain collagen, are better suited for lips than other types of treatments.

Collagen is something that's already in your skin naturally. Human skin consists of three layers -- the epidermis, the dermis and the hypodermis. Collagen is a protein found in the dermis, the middle layer, and it provides skin with structure and shape. As a person gets older, however, collagen production starts breaking down. Some of the elasticity in your skin disappears, which results in wrinkles in your skin or less shape to your lips [source: Shuman].

In recent years, collagen injections have been a common way to get that plumpness back into your lips. There are basically two major options when it comes to collagen fillers: bovine-derived or human-derived. As the name implies, bovine-derived collagen comes from cows. Don't let this turn you off, though. When done properly by your doctor, bovine-derived collagen can work just as well as its counterpart, which is grown from human cells in a lab [source: Nazario].

To learn about the cost of collagen lip injections, move ahead to the next section.