Human hair grows through ‘pulling’ not push – study

Scientists have found that human hair growth does not grow by being pushed out of the root; it's actually pulled upward by a force associated with a hidden network of moving cells. The findings challenge decades of textbook biology and could reshape how researchers think about hair loss and regeneration.

The team, from L'Oréal Research & Innovation and Queen Mary University of London, used advanced 3D live imaging to track individual cells within living human hair follicles kept alive in culture. The study, published in Nature Communications, shows that cells in the outer root sheath - a layer encasing the hair shaft - move in a spiral downward path within the same region where the upward pulling force originates from.

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, the researchers blocked cell division inside the follicle, expecting hair growth to stop. Instead, growth continued nearly unchanged. But when they interfere with actin - a protein that enables cells to contract and move - the hair growth rate dropped by more than 80 per cent. Computer models confirmed that this pulling force, correlated with coordinated motion in the follicle's outer layers, was essential to match the observed speeds 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."

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.