LONDON — Scientists have raised hopes of a cure for baldness after discovering that hair can be regrown. An American team made the advance after identifying a mechanism that relies on reawakening dormant genes. Follica Inc. has licensed the technology in the hope of developing new treatments for baldness.

While adult mammals can repair injuries to themselves, they lack the ability to rebuild lost parts of their bodies — unlike newts and salamanders, which can sprout limbs. Experts previously thought that it was equally impossible for adult skin to regenerate hair follicles.

Now it seems adult mice can indeed regenerate hair follicles, according to a study published today by Dr. George Cotsarelis of University of Pennsylvania School of Medicine, Philadelphia, and colleagues in the journal Nature.

Rather than turning on stem cells, as thought, the method works by reactivating genes used during development of the embryo. If researchers can control hair growth, then they may potentially find cures for people with hair and scalp disorders, such as scarring alopecia, where the skin scars and there is hair overgrowth.

Wounding, they report, triggers new hair-producing follicles to form, a claim that was first made half a century ago after experiments on rabbits but which was written off as unconvincing. The new work shows that the effect is real and a consequence of a molecular signal involving a protein called wnt. Following wounding, the signal increases the number of regenerated hair follicles.

By introducing more wnt, the researchers could make skin regenerate instead of just repair, doubling the number of new hair follicles. The team also shows that turning off wnt signaling prevents new follicles from forming.

“Wound healing triggered an embryonic state in the skin which made it receptive to receiving instructions from wnt proteins,” Dr. Cotsarelis said. The same mechanism could be used to cut scarring, too. “We can influence wound healing with wnts or other proteins that allow the skin to heal in a way that has less scarring and includes all the normal structures of the skin, such as hair follicles and oil glands, rather than just a scar,” Dr. Cotsarelis explained.

“This is an extremely exciting discovery and shows promise for treatment of follicular disorders such as hair loss and unwanted excess hair,” the director of the University of California at San Francisco Hair Research Center and a scientific advisory board member of Follica, Dr. Vera Price, said.

Dr. Denis Headon of the University of Manchester said: “Up to now we thought that the number of hair follicles we have is set before we were born and can only go downhill from there. This work shows that new hair follicles are made in adult skin, at least when it is healing a wound. It might be simpler than we thought to make new hair follicles as a treatment for hair loss.”