Botox (botulinum toxin type and Myobloc (botulinum toxin type B) are purified forms of bacteria. Soft-tissue fillers include collagen (human or bovine) and hyaluronic acid (Restylane).

How they work: Botox and Myobloc shut down the nerve signals responsible for the muscle contractions that make facial expressions causing wrinkles and furrows. That's why it's more effective as a preventative treatment, says Jeffrey Dover. After about a year, however, existing lines can soften and smooth out, he says. (They will return once you stop getting injections.) One treatment usually lasts three to four months. Fillers are injected into the skin to plump up wrinkles. Bovine collagen has been used for more than 25 years. Two skin tests determine whether you're allergic to it, and the effects typically last four months. With human collagen, bioengineered from infant foreskin tissue, there's no allergy test or waiting time necessary between the initial consultation and treatment. Hyaluronic acid (Restylane) is found naturally in the skin. Because it lasts longer (six to nine months) and allergic reaction is rare, it appears to be a better filler than collagen. If necessary, doctors can also remold Restylane several weeks after injecting it. One drawback: It may cause swelling that lasts one to three days.

On the horizon: The most promising new fillers are Sculptra, Perlane, and silicone. The FDA is reviewing study results for Sculptra, a deep-tissue filler made of poly-L-lactic acid. Sculptra plumps up thin or sunken cheeks. Perlane, like Restylane, is made of hyaluronic acid, but in larger particles, which fill deeper wrinkles. Jeffrey Dover anticipates FDA approval in the next year or so. Silicone, once used as a filler, was banned in 1992 for safety and efficacy reasons. Since then, doctors have developed a better, medical-grade injectable form that's approved for treating retinal detachment. The FDA is monitoring preliminary studies of its cosmetic uses. Unlike most fillers, silicone is permanent, which makes it appealing only to some. "Permanent fillers have permanent side effects," says Dover. These could include a lumpy look. "I'd never choose it for myself," he says, "but my patients who hate to come back for repeat collagen treatments think it's wonderful."