An inability of stem cells in the scalp to develop into the type of cells that make hair follicles may be an underlying cause of male-pattern baldness, according to a new study.

The discovery gives hope that people who are bald could regrow their hair with a future treatment, said study researcher Dr. George Cotsarelis, a professor of dermatology at the University of Pennsylvania.

In people who are bald, hair follicles have shrunken and become microscopic, Cotsarelis said. And scientists long thought that bald people also had a depletion of hair follicle stem cells, which are necessary to grow hair.

But the new study shows that bald people have the same number of stem cells as those with hair. So if scientists could coax the stem cells into producing more hair follicle progenitor cells, then it would be possible to generate bigger hair follicles that could grow hair, he said.

If the hair follicle stem cells were "gone or markedly depleted, it would be much more daunting, but because they're there, it tells us there should be a way" to re-grow hair, Cotsarelis told MyHealthNewsDaily. "It's not impossible. It gives you hope."

The study was published today (Jan. 4) in the Journal of Clinical Investigation.

Counting cells

Cotsarelis and his colleagues analyzed skin cells from the bald and non-bald parts of the scalp of people with androgenetic alopecia, the technical name for male-pattern baldness.

They ran the scalp cells through a machine that tagged each cell with a marker. By using different markers to distinguish between stem cells and hair follicle progenitor cells, scientists were able to count the number of each type.

They found there were the same number of stem cells in the skin from bald scalps as there were in the skin from the non-bald scalps. However, there were fewer hair follicle progenitor cells in the skin from the bald scalps than the skin from the non-bald scalps.

In other words, the scientists found that baldness was occurring because the stem cells were unable to complete their normal development and become hair follicle progenitor cells.

A different approach

Currently, Rogaine and Propecia are the only two treatments for baldness approved by the Food and Drug Administration, Cotsarelis said. They are effective for maintaining hair already on the scalp, but aren't that effective in re-growing hair, he said.

Propecia, for example, blocks testosterone's effect on hair follicles — the hormone can reduce big hair follicles to small ones. But the drug doesn't actually bring back the big follicles, Cotsarelis said.

To regrow hair that has been lost, you'd need a drug that "can make a small follicle into a big follicle," he said.

"If we figure out what the signals are, and the factors that are necessary to activate the stem cells to make progenitor cells, there should be a way to reverse those small follicles to make them large," he said.

Pass it on: Bald people have hair follicle stem cells, and researchers say finding this means there is hope for a treatment that could regrow hair.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.