Researchers from L'Oréal Research & Innovation and Queen Mary University of London used advanced 3D live imaging to observe individual cells inside living human hair follicles maintained in laboratory culture. Their findings, published in Nature Communications, revealed that cells in the outer root sheath -- a layer encasing the hair shaft -- move along a spiral path downward within the same region where the upward pulling force is generated.

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."

Experiments Reveal the Force Driving Hair Growth

To investigate the mechanism further, the scientists blocked cell division inside the follicle. They expected hair growth to stop if dividing cells were responsible for pushing the hair upward. Instead, the follicles continued growing hair at nearly the same rate.

However, when the researchers interfered with actin -- a protein that allows cells to contract and move -- hair growth slowed dramatically, dropping by more than 80 per cent. Computer simulations supported the findings, showing that the pulling force created by coordinated movement in the outer layers of the follicle was necessary to match the observed speed of hair growth.

Advanced Imaging Captures Cell Motion in Real Time

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 Follicle Mechanics

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 understanding of how hair follicles function may create opportunities to study hair disorders, test new medications, and advance work in tissue engineering and regenerative medicine."

Although the experiments were conducted on human hair follicles grown in laboratory culture, the findings provide new insights into the biology of hair and regenerative medicine. The researchers suggest that understanding the physical forces inside follicles could help scientists design treatments that target both the mechanical and biochemical environment of the follicle. In addition, the new imaging approach may allow scientists to test potential drugs and therapies on living follicles.

Biophysics Offers New Insights Into Everyday Biology

The study also underscores the expanding influence of biophysics in modern biology. It demonstrates how tiny mechanical forces at the microscopic level can shape the growth and behavior of structures in the human body.