Two board-certified dermatologists told Yahoo Shopping that GHK-Cu, the copper peptide that turns high-concentration serums a distinctive blue, is the most underrated ingredient in the current peptide boom, while stopping well short of calling it a retinol substitute.

GHK-Cu appears on labels as copper tripeptide-1. It is three amino acids, glycine, histidine and lysine, bound to a single copper ion, and Dr. Alexandra Bowles of Mona Dermatology describes it as a copper-binding peptide the body produces naturally, with production slowing with age in the same way collagen production does. The copper bond is what gives the serums their color.

An accidental discovery

The origin story is the part the dermatologists keep coming back to. Dr. Mona Foad, also of Mona Dermatology, says GHK-Cu was identified in the 1970s after Dr. Loren Pickart noticed that blood plasma from younger donors triggered stronger tissue regeneration in liver studies than plasma from older donors.

"It wasn't invented for skin care. It was found because of what it does in the body," Foad says. That is a genuinely unusual provenance in a category where most actives were formulated backward from a marketing claim.

Carrier, not signal

Most peptides in cosmetics are signal peptides, which Foad compares to sending a cell a text message. GHK-Cu is a carrier peptide, delivering a mineral that the skin's own repair enzymes need to function, and she says that mechanism does something retinol does not: research suggests it works on both collagen building and the regulation of collagen breakdown.

She expects it to be one of the bigger skin care stories of the next few years. She also says plainly that it might help with fine lines and will not erase deep wrinkles, which is more restraint than most ingredient hype allows.

Where the evidence is strongest

Wound healing is the best supported use, Foad says, because GHK-Cu was used in surgical and wound settings before it ever reached a serum. Collagen and elastin support is reasonably well documented. The antioxidant claim is the weakest of the three, and Bowles calls it a supportive property rather than the main reason to reach for it.

Bottom line

Bowles's advice is to read the ingredient list rather than the front of the bottle, and to check that copper tripeptide-1 sits reasonably high in it. Serums cited in the piece run from $12 to $62, and concentration, not price, is what varies most.