A previously unknown network of cells plays a crucial role in how hair emerges from the follicle, according to a new study that could rewrite scientific textbooks and lead to new treatments for hair loss.
Until now, it was believed that hair grows because it is “pushed” upward from the root. However, the new research, using advanced three-dimensional imaging, revealed that each hair is actually pulled upward by a coordinated network of moving cells.
“For decades, we thought hair was pushed outward by the dividing cells in the hair bulb. We discovered, however, that it is actively pulled upward by the surrounding tissue, which functions almost like a tiny motor,” says Ines Sequeira from Queen Mary University in London, one of the study’s authors, published in Nature Communications.
The study
In the study, scientists blocked cell division within the hair follicle and expected hair growth to slow or stop. Instead, they observed that growth continued at nearly the same rate. However, when they interfered with the actin protein, which allows cells to contract and move, hair growth decreased by more than 80%.
The model
Computer simulations confirmed that the pulling force of actin, combined with the coordinated cellular mechanism in the outer layers of the follicle, is crucial for the speed at which hair moves upward.
“This approach reveals a spiral downward movement of the outer root sheath cells entering the lower bulb region. We propose a mechanistic model in which a pulling force generated by the outer root sheath contributes to hair emergence,” the study explains.
Using advanced real-time 3D time-lapse microscopy, researchers were able to observe the complex and dynamic biological processes within the hair follicle. This technique allowed them to see cell divisions that could not have been inferred from individual observations.
“This approach allowed us to model the forces produced locally,” said Nicolas Tissot, a member of the research team. Observations showed that hair growth is not determined solely by cell division, but that the outer root sheath “actively pulls the hair upward,” according to Dr. Thomas Bornsklogl, also a team member.
The scientists hope that this new understanding of the mechanical forces governing hair growth will help design new hair loss treatments that target the follicles directly.
“This new view of follicle mechanics opens up fresh opportunities for studying hair disorders, drug testing, and advances in tissue engineering and regenerative medicine,” said Bornsklogl. The imaging method used in the study may also enable live testing of different drugs and therapies, according to the researchers.