The doctors interviewed agreed that while the optimal age for a patient to begin getting fillers is in the 40s to early 50s, all had treated younger patients on a case-by-case basis, depending on their situations and expectations. "In a place like Hollywood, people want to look good in the 20s and 30s," says Dr. Fisher. "It's easy to get frown lines just by expression, or exercising hard."

But getting doctors to concur on much else isn't easy. All have their opinions on the various fillers, and often they differ. Take Evolence, which contains porcine collagen. Dr. Ariel Ostad says it's "amazing" because it doesn't cause bruising. But Chicago dermatologist and cosmetic surgeon Dr. Edward Lack, formerly president of the American Academy of Cosmetic Surgery, says Evolence is a "me too" product that has "no advantages" over what is already on the market.

And while Dr. Fisher feels that Perlane lasts longer than Restylane, Dr. Lack disagrees. Medicis Pharmaceutical, which has the license to market Restylane and Perlane in North America, prefers to stay out of the fray: "We only promote what is on label," says spokesperson Kara Stancell. Perlane is FDA approved to last for only for six months, while Restylane is approved for lasting up to 18 months (with repeat injections). While some products, like Radiesse, claim to promote collagen reproduction, Dr. Tehrani and Dr. Lack make the case that any injection will generate collagen, since the body produces collagen to wall off the foreign substance.

The truth is likely somewhere in between: When you're dealing with patients' individual skin textures, age, sun damage and genetic and metabolic factors, not to mention a doctor's preferences and skill with injectables, the filler that works best is judged on a case-by-case basis.