"It is inefficient, but it's enough to increase cell turnover," he said. "It is sort of crude, and we were able to show that."
Scientific data do exist on epidermal growth factor, some of it published by Brown in peer-reviewed medical journals before he founded ReVive.
But without published studies on the creams themselves, it's impossible to know whether the epidermal growth factor in them is effective. "The usual difficulty with such products is whether or not the large protein molecules such as the epidermal growth factor remain active in the formulation and, if they are active, whether they actually get delivered across intact skin," Medlicott said.
Telomerase, another ingredient in Peau Magnifique Youth Recruit, is "an enzyme that activates and differentiates dormant adult stem cells into brand new skin cells" and "repairs DNA fragmentation," according to the product's press materials.
But what effect does the telomerase in this product have on a customer's skin? "We don't know exactly," Brown said. "We know stem cells line the hair follicle and sweat glands. They are on the surface. We don't know if it has an effect on those cells."
Brown added that ReVive tests the safety of each product it puts on the market.
Perricone MD Cosmeceuticals stated in a company blog post that an ingredient called DMAE in its Face Finishing Moisturizer "allows for face-lift-like benefits as well as other long lasting anti-aging contributions when applied to the face or taken as a supplement."
But the product packaging does not state how much DMAE is in the cream, which sells for $65 for 2 ounces at Sephora.
A search of medical literature turned up no clinical trials on the product to show it works, though several small published studies have looked at DMAE's effect on skin cells and skin and suggested that it can help with firming.
How? Pharmacologist Francois Marceau at Laval University in Quebec City found that when skin cells were exposed to DMAE, tiny compartments inside the cells swelled up and some cells died. The swelling, he said, is a likely explanation for the skin thickening, or firming.
"This is not necessarily very dangerous, but has not been properly analyzed scientifically," Marceau, whose study was published in 2007 in the British Journal of Dermatology, wrote in an e-mail. "I would like to see them follow formal FDA rules for drug development."
Perricone MD Cosmeceuticals responded: "We do consumer use studies to support our claims, and our positioning has always stood that we strive to underpromise and overdeliver."
Dermatologists interviewed for this story said most skin creams are harmless. If you like a product, enjoy it, they said, but realize your skin likely won't be miraculously transformed.
"Go ahead, but it won't do much more than a moisturizer that is a lot less expensive," Yoo said. "It won't be any better than Neutrogena or Cetaphil for less than a 10th of the price or a 100th of the price."