Under the Federal Food, Drug and Cosmetic Act, the FDA legally defines products by their intended uses. Drugs are defined as products intended for treating or preventing disease and affecting the structure or any function of the body. A medical device is a product that also is intended to affect the structure or function of the body, but which does not achieve its primary intended purposes through the chemical action of a drug--nor is it dependent on being metabolized.

The hyaluronic acid in Restylane, although biosynthetically produced (formed of chemical compounds by the enzyme action of living organisms), is almost identical to that in all living organisms. Hyaluronic acid is a structural component of skin that creates volume and shape. Concentrations of hyaluronic acid throughout the body decline with age, causing undesirable changes in the skin. Restylane binds to water and provides volume to easily fill in larger folds of skin left by tissue loss around the mouth and cheeks. "This makes it a structural action," says Rhodes, "much like a chin implant."

In contrast, cosmetics are defined as substances that cleanse, beautify, promote attractiveness, or alter the appearance, without affecting the body's structure or function. This definition includes skin-care products such as creams, lotions, powders and sprays; perfume; lipstick; fingernail polish; and more.

Different laws and regulations apply to each type of product. Some products must comply with the requirements for both cosmetics and drugs. This happens when a product has two intended uses, such as an antidandruff shampoo. A shampoo is a cosmetic because it is intended to clean hair. An antidandruff shampoo is a cosmetic and a drug because it is intended to treat dandruff (which affects the follicles where the hair is formed) and clean hair.