Researchers have found a way to encourage new hair growth in mice, and they're hoping something similar can be done with humans.
Hair comes from a complex mini-organ in the skin called a hair follicle. According to traditional thinking, new hair follicles only form in junior mammals. Once you're an adult, and you lose some hair follicles, you're out of luck in the hair department.
Now it's a funny thing about dogma, it tends to color the way you look at the world. Jonathan Vogel is a dermatologist at the National Institutes of Health. He says scientists who study how wounds heal relied on dogma to explain something they always see.
"We know when we make wounds in mice that eventually that area is replaced with hair," Vogel says. "It's not like the mice typically go round with large patches of skin without hair. But I guess we assumed that that was not new hair." Instead, it was thought that areas that previously had hair migrated in as the wound healed.
But as George Cotsarelis reports in the current issue of Nature, that explanation appears to be wrong. Cotsarelis is a stem-cell biologist at the University of Pennsylvania. He, too, noticed that hair appeared in a wounded area. But he also knew from his stem-cell work that hair follicles typically come from something called a bulge stem cell. The hair forming after wounds was not coming from bulge stem cells. Something else was happening.
"It really tells us that the skin is sort of reprogramming cells that normally don't make hair follicles to make hair follicles," Cotsarelis says.
In other words, not only were these hair follicles new, they were forming in a totally new way.
Now you might think it somewhat surprising that scientists had overlooked the fact that new hair follicles were forming in response to a wound.
"Fifty years ago, some doctors did observe this in the rabbit as well as in the human," says Cheng-Ming Chuong, a pathologist at the University of Southern California.
But even then, dogma was so strong that they dismissed the results.
But Chuong says there's another factor. In order to see the new hair, Cotsarelis had to make a fairly large wound and leave it open. The new hair didn't grow when the wound was smaller. Chuong says that may explain why doctors don't see new hair growing in patients with large wounds.
"People would try to get the wound closed, as fast as you can. So that in a way, (they would) make the condition not ideal for hair regeneration," Chuong says. The wound has to be kept open long enough for the hair follicles to appear.
So the bad news for humans who might like to grow a little hair is that for the moment, at least, a substantial wound appears to be necessary. But the good news, says Cotsarelis, is that it may be possible to figure out how to switch on the molecular pathways that trigger hair growth without inflicting an injury.
And there's even a more promising outcome.
"If you look at the molecular pathways during hair follicle development, many of them overlap with limb development," Cotsarelis says.
So maybe one day, in addition to new hair, people could grow new fingers or arms.
"That's kind of pie in the sky, but you never know where these advances come from, and we're always thinking about things like that, too," Cotsarelis says.