New research suggests that human hair does not grow by being pushed out from the root, as was long believed. Instead, scientists discovered that hair is pulled upwards by forces created by a hidden network of migrating cells within the hair follicle. The discovery challenges decades of biology textbook explanations and could impact how researchers approach hair loss and hair regrowth.
Researchers from L’Oréal Research & Innovation and Queen Mary University of London used advanced 3D live imaging to observe individual cells within living human hair follicles maintained in laboratory culture. Their findings are: nature communicationsfound that cells within the outer root sheath (the layer that envelops the hair shaft) move downward along a helical path within the same region where the upward pulling force occurs.
Dr. Ines Sequeira, Reader in Oral and Skin Biology at Queen Mary University and one of the lead authors, said: “Our findings reveal an interesting movement within the hair follicle. For decades, it was thought that hair was pushed out by dividing cells within the hair bulb. Instead, we now find that the hair is actively pulled upwards by the surrounding tissue, which acts almost like a tiny motor.”
Experiment reveals power to promote hair growth
To further investigate this mechanism, scientists blocked cell division within the follicle. They predicted that if the dividing cells were responsible for pushing the hair upwards, hair growth would stop. Instead, the hair follicles continued to grow hair at roughly the same rate.
But when the researchers interfered with actin, a protein that allows cells to contract and move, hair growth slowed dramatically, decreasing by more than 80%. Computer simulations corroborated this finding and showed that matching the observed hair growth rate requires a pulling force produced by the coordinated movement of the outer layer of the hair follicle.
Capture cell movement in real time with advanced imaging
Dr. Nicolas Tissot, lead author from L’Oréal’s advanced research team, said: “We are using a new imaging technique that enables 3D time-lapse microscopy in real time. Time-lapse microscopy is essential to truly unravel the complex and dynamic biological processes within the hair follicle, revealing important cell dynamics, migration patterns, and rates of cell division that cannot be observed using other methods, which were impossible to extrapolate from discrete observations.This approach allows us to model locally generated forces.
Rethinking how hair follicles work
Dr. Thomas Bornschlaegl, another lead author from the same L’Oréal team, added: “This reveals that hair growth is not driven solely by cell division. Instead, the outer root sheath is actively pulling the hair upwards.” This new understanding of hair follicle function could create opportunities to advance hair disease research, new drug testing, and research in tissue engineering and regenerative medicine. ”
The experiments were performed on human hair follicles grown in laboratory cultures, and the results provided new insights into hair biology and regenerative medicine. The researchers suggest that understanding the physical forces inside the follicle could help scientists design treatments that target both the mechanical and biochemical environments of the follicle. Additionally, new imaging approaches may allow scientists to test potential drugs and treatments on living follicles.
Biophysics brings new insights to everyday biology
This study also highlights the growing influence of biophysics in modern biology. This shows how small mechanical forces at the microscopic level can shape the growth and behavior of structures in the human body.
