When Eva Campbell-Morales was in her early 40s, she noticed that her face, which was naturally thin, was suddenly starting to look gaunt and old. “Being thin meant I looked great in my jeans, but my face looked like the crypt keeper,” said Ms. Campbell-Morales, 51, an actress and Spanish translator. She saw several doctors in pursuit of a traditional face-lift, but no one would agree that was what she needed. Finally, she saw Dr. Nathan Newman, a Beverly Hills, Calif., dermatologist, who persuaded her to try a newer procedure called a “stem-cell face-lift.”

“The results were phenomenal,” Ms. Campbell-Morales said, who later posted a video on YouTube about the experience. “Afterward, my face had more structure and all of the hollow areas were filled in.”

The term “stem-cell face-lift” is something of a misnomer. A conventional face-lift requires surgically cutting, lifting and sewing sagging skin, while this procedure is typically nonsurgical, involving fat injections designed to plump up the skin and restore the face’s youthful volume.

The stem-cell face-lift starts with liposuction to harvest fat from a place that has extra (like the stomach or thighs) that can later be injected into a place that doesn’t have enough (like the hollows of the cheeks or around the eyes).

So where, exactly, do the stem cells come into play? That is the million-dollar question. Or more accurately, the $5,000 to $10,000 question, since that’s about how much people are paying for the procedure. And the answer very much depends on whom you ask.

“I’m convinced that 90 percent of the doctors promising this are just taking the fat, spinning it in a centrifuge a bit and injecting it into the face,” said Dr. Karol Gutowski, a plastic surgeon in Northbrook, Ill. “They’re essentially doing fat grafting, which has been around decades, and any stem cells that happen to be in that fat are just coming along for the ride.”

Proponents of stem-cell face-lifts, not surprisingly, have a very different take. Dr. Newman, who performed the procedure on Ms. Campbell-Morales, said he has been working on his stem-cell procedure for more than a decade, using what he described as a mechanical process that breaks up collagen and allows the stem cells to be separated out. He is convinced that adding extra stem cells to the injected fat is the ticket to better skin. “The youthful glow comes back to skin because of growth factors that are produced from the stem cells,” he said. And that, in his opinion, doesn’t happen by injecting fat alone.

Stem cells are found in many different tissues throughout the body. They are often referred to as “undifferentiated cells.” That means they are essentially biological blank slates that are capable of becoming another differentiated type of cell — like a skin cell, a fat cell or a muscle cell.

Researchers have been exploring the regenerative properties of adult stem cells (and the more controversial embryonic stem cells) for decades, experimenting with their potential to generate tissue that could help heal conditions from heart disease to spinal cord injury. For the increasingly popular aesthetic procedures like the stem-cell face-lift, the source of these stem cells is normally adipose (fat) tissue.

For critics of the stem-cell face-lift, the main problem isn’t necessarily the use of stem cells, but that claims like Dr. Newman’s are backed up mostly by anecdotal evidence. “You won’t find a bigger proponent of stem-cell technology than me,” said Dr. Peter Rubin, a director of the Adipose Stem Cell Center at the University of Pittsburgh. “But I’m also a fan of something called evidence-based medicine. If doctors are making claims of better outcomes, we need hard data that supports that.”

In pursuit of that hard data, Dr. Rubin was a chairman of a joint task force with Dr. Gutowski to look into the scientific evidence assessing both the safety and efficacy of stem-cell use in aesthetic procedures.

And in May 2011, the task force (a collaboration between the American Society for Plastic Surgeons and the American Society for Aesthetic Plastic Surgery) issued a position statement on the topic. After going through thousands of peer-reviewed articles published in medical journals on the use of stem cells in aesthetic procedures, they found only about a dozen that provided any “real clinical data on aesthetic use,” Dr. Rubin said. “Very little of this research has been done in randomized controlled settings.”

That would involve doing experiments like treating one-half of the face with traditional fat injections and the other with stem-cell-enriched fat — and having ways to measure any qualitative skin changes accurately (as opposed to relying on before-and-after photos or patient feedback).

“We need studies that look at exactly how the skin tissue responds and whether more volume is retained if you use more stem cells,” Dr. Gutowski said. “We’re not seeing that research yet.”

For now, the task force is urging caution on all aesthetic stem-cell procedures, and a hearty dose of “let the buyer beware.” The report states “the marketing and promotion of stem cell procedures in aesthetic surgery is not adequately supported clinical by evidence at this time.”

But that is not to say that there isn’t potential here. “Stem cells in fat are very powerful releasers of growth factors that enhance tissue healing and can induce the growth of new blood vessels in the tissue,” Dr. Rubin said. His lab is in the midst of a clinical trial, financed by the National Institutes of Health, on the use of stem-cell-enhanced fat grafting versus nonenhanced fat grafting for treating facial deformities on wounded soldiers. When the trial is complete, the results will help either bolster or diminish the case for procedures like the stem-cell face-lift.

Google the term “stem-cell face-lift” and you’ll get dozens of pages of results — including several for doctors advertising their version of the procedure. For many surgeons, that sort of self-promotion is a giant red flag. Regardless of the future potential for these procedures, Dr. Gutowski takes issue with anyone trying to trademark their technique. “That’s a pure marketing gimmick,” he said. “That’s not medicine.”