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When the stem cells in your hair follicles age, they turn into skin, not hair! And slowly, they shrink and disappear.

This study was pioneered by a Tokyo Medical and Dental University researcher.

Hair follicle stem cells are unlike other standard stem cells, such as the ones found in the blood or intestinal lining. They regenerate cyclically. They first have an active growth phase, and then undergo a dormant phase, ceasing the production of hair. Hence, it is a unique growth cycle that makes hair follicle stem cells a new and unique model that shows the secrets behind "stem cell regulation and hair loss".

"Previously, people knew that when we age, the hair becomes thinner," said Cheng-Ming Chuong, a biologist who was not a member of the team. But at the cellular and molecular level, "there's not enough understanding."

Stem cell growth cycles were probed in mice by Emi Nishimura, head of the study. He discovered that DNA damage sparked off the damage of the Collagen 17A1 protein. It hence triggers the transformation of stem cells into epidermal keratinocytes, or stem cells that can be sloughed off from the surface of the skin.

"When damaged cells deplete that niche of Collagen 17A1, they alter their own signaling environment," said Maksim Plikus, another biologist who was not part of the team.

Nishimura examined the hair follicles of scalps of women aged 22 to 70, showing that follicles in subjects aged over 55 years were much smaller, with lower Collagen 17A1 levels.

"We assume that ... aging processes and mechanisms [similar to those in the mice] explain the human age-associated hair thinning and hair loss," Nishimura said in a press release.

The results can enable scientists to use Collagen 17A1 to address hair loss.

The findings were published in the Feb.5,2016 issue of Science.