Researchers from the University of Pennsylvania School of Medicine have found that stem cells play a vital role in male pattern baldness. 

George Cotsarelis, MD, study leader and chair of the Department of Dermatology at the University of Pennsylvania School of Medicine, along with a team of researchers, have discovered that the amount of stem cells on the scalp may determine male pattern baldness. 

Researchers came to this conclusion after comparing samples from men who were going through hair transplants. When looking at samples from both bald parts of the scalp and non-bald parts of the scalp, both had the same number of stem cells. 

"We asked: 'Are stem cells depleted in bald scalp?'" said Cotsarelis. "We were surprised to find the number of stem cells was the same in the bald part of the scalp compared with other places, but did find a difference in the abundance of a specific type of cell, thought to be a progenitor cell. This implies that there is a problem in the activation of stem cells converting to progenitor cells in bald scalp."

Cotsarelis and his team of researchers studied their theory a little closer, and found that hair follicles shrink rather than disappear in male pattern baldness. So hair is available in bald spots of the scalp, but it's microscopic compared to other non-balding parts due to the stem cells' problem with activation. 

Cotsarelis found similar results in 2007 while studying hair follicles in adult mice. He discovered that “re-awakening” dormant genes in developing embryos could regenerate hair follicles. They used wound healing in these models to manipulate certain traits, and by stimulating these once-active genes; stem cells formed new hair follicles. 

Researchers are unsure as to why stem cells refuse to convert into the progenitor cells to maintain a certain amount of hair follicles, but they remain hopeful due to the fact that both areas on the scalp have the same number of stem cells. That way, they can find ways to stimulate stem cell conversion and re-grow the hair in bald areas. 

In addition to this study, Cotsarelis and his team would like to study female pattern baldness as well for comparison purposes. This could lead to a larger understanding of why the hair shrinks in humans, and could lead to the development of cell-based treatments for male and possibly female pattern baldness.