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A new imaging study challenges long-standing ideas about how hair grows and could lead to new treatments for hair loss.
Scientists have discovered that human hair does not emerge because it is pushed upward from the root. Instead, it is pulled along by forces generated by a previously unseen network of moving cells. This finding overturns long held ideas in biology and may change how scientists approach hair loss and tissue regeneration.
A hidden force drives hair growth
Researchers from L’Oréal Research & Innovation and Queen Mary University of London used advanced 3D live imaging to observe individual cells inside human hair follicles that were kept alive in laboratory culture. Their study, published in Nature Communications, revealed that cells in the outer root sheath (the layer that surrounds the hair shaft) move in a downward spiral within the same region that produces the upward pulling force responsible for hair growth.
Dr Inês Sequeira, Reader in Oral and Skin Biology at Queen Mary and one of the lead authors, said, “Our results reveal a fascinating choreography inside the hair follicle. For decades, it was assumed that hair was pushed out by the dividing cells in the hair bulb. We found that instead that it’s actively being pulled upwards by surrounding tissue acting almost like a tiny motor.”
To test this idea, the team blocked cell division inside the follicle, expecting hair growth to slow or stop. Instead, growth continued at nearly the same rate. However, when the researchers disrupted actin, a protein that allows cells to contract and move, hair growth fell by more than 80 percent. Computer simulations confirmed that this pulling force, linked to coordinated movement in the follicle’s outer layers, was necessary to explain the observed speed of hair movement.
Dr. Nicolas Tissot, the first author, from L’Oréal’s Advanced Research team said: a “We use a novel imaging method allowing 3D time-lapse microscopy in real-time. While static images provide mere isolated snapshots, 3D time-lapse microscopy is indispensable for truly unraveling the intricate, dynamic biological processes within the hair follicle, revealing crucial cellular kinetics, migratory patterns, and rate of cell divisions that are otherwise impossible to deduce from discrete observations. This approach made it possible to model the forces generated locally.”
Rethinking hair disorders and regeneration
Dr. Thomas Bornschlögl, other lead author, from the same L’Oréal team adds: “This reveals that hair growth is not driven only by cell division – instead, outer root sheath actively pull the hair upwards.” This new view of follicle mechanics opens fresh opportunities for studying hair disorders, testing drugs, and advancing tissue engineering and regenerative medicine.”
While the research was carried out on human follicles in lab culture, it offers new clues from hair science and regenerative medicine. The team believes that understanding these mechanical forces could help design treatments that target the follicles physical as well as biochemical environment. Furthermore, the imaging technique developed will allow live testing of different drugs and treatments.
The study also highlights the growing role of biophysics in biology, showing how mechanical forces at microscopic scale shape the organs we see every day.
Reference: “Mapping cell dynamics in human ex vivo hair follicles suggests pulling mechanism of hair growth” by Nicolas Tissot, Gaianne Genty, Roberto Santoprete, Frederic Baltenneck, Sebastien Thibaut, Jean-Francois Michelet, Inês Sequeira and Thomas Bornschlögl, 21 November 2025, Nature Communications.
DOI: 10.1038/s41467-025-65143-x
I.S. was supported by the Barts Charity (MGU045/ G-001524) and the Royal Society (RGS/R2/202291).
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