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By Melissa Fleur Afshar
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Decades of textbook biology may need to be rewritten after an imaging study has revealed that hair does not grow by being pushed out from the root, as previously believed—but is pulled upward by coordinated moving cells.
The study by scientists from L'Oréal Research & Innovation and Queen Mary University of London, England, used advanced 3D live imaging to observe living human hair follicles in lab culture. The findings not only alter the basic mechanics of hair development but may open up new strategies in regenerative medicine and treatments for hair loss.
“Our results reveal a fascinating choreography inside the hair follicle," paper author and professor Inês Sequeira said in a statement. "For decades, it was assumed that hair was pushed out by the dividing cells in the hair bulb.
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"We found that instead that it’s actively being pulled upwards by surrounding tissue acting almost like a tiny motor.”
To test their theory, the scientists blocked cell division inside the hair follicle, expecting that hair growth would stop if the traditional 'pushing from below' model were true. But hair growth continued at nearly the same pace. When they instead blocked actin—a protein that helps cells move—the growth rate dropped by more than 80 percent.
Computer dynamics simulations supported what the scientists saw under the microscope. Only models that included a pulling force from the outer sheath could explain how fast the hair moved upward.
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“We use a novel imaging method allowing 3D time lapse microscopy in real-time," Dr. Nicolas Tissot, the first author, from L’Oréal’s Advanced Research team, said in a statement.
"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.”
The discovery could eventually help scientists develop new treatments for hair loss. By focusing on the pulling mechanism rather than just promoting cell division, future therapies might better support hair growth in people experiencing thinning or balding.
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Reference
Tissot, N., Genty, G., Santoprete, R., Baltenneck, F., Thibaut, S., Michelet, J.-F., Sequeira, I., & Bornschlögl, T. (2025). Mapping cell dynamics in human ex vivo hair follicles suggests pulling mechanism of hair growth. Nature Communications, 16(1). https://doi.org/10.1038/s41467-025-65143-x
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