A pioneering technique that generates new hair follicles could help to banish baldness, research suggests.
For the first time, scientists have shown that it is possible to renew follicles capable of sprouting human hair.
The follicles grow naturally from clumps of cells called dermal papillae that play a pivotal role in hair growth.
Scientists harvested dermal papillae from seven human donors, cloned them in the laboratory, and transplanted them into human skin grafted onto the backs of mice.
In five of the tests, the transplants resulted in new hair growth that lasted at least six weeks. DNA analysis confirmed that the new hair follicles were human and a genetic match to the donors.
Although the research is at an early state, the British and American team is confident clinical trials could begin "in the near future".
Professor Angela Christiano, from Columbia University Medical Centre in New York, said: "Current hair-loss medications tend to slow the loss of hair follicles or potentially stimulate the growth of existing hairs, but they do not create new hair follicles. Neither do conventional hair transplants, which relocate a set number of hairs from the back of the scalp to the front.
"Our method, in contrast, has the potential to actually grow new follicles using a patient's own cells. This could greatly expand the utility of hair restoration surgery to women and to younger patients - now it is largely restricted to the treatment of male-pattern baldness in patients with stable disease."
Dermal papillae are small cells found at the base of hair follicles. The research develops earlier work led by Professor Colin Jahoda at the University of Durham showing that in rodents dermal papillae could easily be harvested and transplanted back into the skin.
In rodents, the transplanted cells tended to clump together spontaneously and reprogramme the recipient's skin to grow new hair follicles.
The new research followed the lessons learned in rodents by encouraging human cells to clump together in the same way.
"Dermal papilla cells give rise to hair follicles, and the notion of cloning hair follicles using inductive dermal papilla cells has been around for 40 years or so," said Prof Jahoda, who co-led the research published in the journal Proceedings of the National Academy of Sciences.
"However, once the dermal papilla cells are put into conventional, two-dimensional tissue culture, they revert to basic skin cells and lose their ability to produce hair follicles. So we were faced with a Catch-22: how to expand a sufficiently large number of cells for hair regeneration while retaining their inductive properties."
The technique may offer new hope to women as well as men who suffer from baldness, say the scientists. It also raises the prospect of new treatments for burns victims.
"About 90% of women with hair loss are not strong candidates for hair transplantation surgery because of insufficient donor hair," said Prof Christiano. "This method offers the possibility of inducing large numbers of hair follicles or rejuvenating existing hair follicles, starting with cells grown from just a few hundred donor hairs. It could make hair transplantation available to individuals with a limited number of follicles, including those with female-pattern hair loss, scarring alopecia, and hair loss due to burns."
Prof Jahoda said more work was needed to explore the properties of hair generated by newly grown follicles, and the interaction between transplanted dermal papillae and host cells.
He added: "Ultimately we think that this study is an important step toward the goal of creating a replacement skin that contains hair follicles for use with, for example, burn patients."