Hair Growth Isn’t About Pushing – It’s About Pulling, Fresh Research Reveals

For decades, biology textbooks have described hair growth as a process of cells dividing at the base of the hair follicle and pushing older cells upward. However, groundbreaking research published in Nature Communications challenges this long-held assumption, revealing that hair growth is actually driven by a “pulling” force generated by a network of moving cells within the follicle. This discovery, made by researchers from L’Oréal Research & Innovation and Queen Mary University of London, could reshape our understanding of hair loss and pave the way for new regenerative treatments.

The Unexpected Mechanism of Hair Growth

Using advanced 3D live imaging, the research team observed individual cells within living human hair follicles maintained in laboratory culture. Their findings demonstrate that cells in the outer root sheath – the layer surrounding the hair shaft – move in a spiral downward path. This movement generates an upward pulling force that drives hair growth, rather than the previously believed pushing mechanism.

“Our results reveal a fascinating choreography inside the hair follicle,” explains Dr. Inês Sequeira, Reader in Oral and Skin Biology at Queen Mary and one of the lead authors of the study. “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 Confirm the ‘Pulling’ Force

To test their hypothesis, the researchers initially blocked cell division within the follicle, anticipating that hair growth would cease. Surprisingly, hair continued to grow at nearly the same rate, indicating that cell division isn’t the primary driver of hair elongation.

However, when the researchers interfered with actin – a protein crucial for cell contraction and movement – hair growth slowed dramatically, decreasing by more than 80 percent. This finding, coupled with computer modeling, confirmed that the pulling force generated by coordinated movement in the follicle’s outer layers is essential for achieving the observed hair growth speeds.

Advanced Imaging Reveals Cellular Dynamics

The study utilized a novel 3D time-lapse microscopy technique, allowing researchers to observe cellular processes in real-time. Dr. Nicolas Tissot, from L’Oréal’s Advanced Research team, emphasized the importance of this technology: “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.”

Implications for Hair Loss Treatment and Regenerative Medicine

Dr. Thomas Bornschlögl, likewise from L’Oréal’s research 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 hair follicle mechanics opens up potential avenues for studying hair disorders, testing new medications, and advancing tissue engineering and regenerative medicine.

Although the experiments were conducted on hair follicles grown in a laboratory setting, the findings provide valuable insights into the biology of hair growth and could lead to the development of more effective treatments for hair loss. Understanding the physical forces within follicles may allow scientists to target both the mechanical and biochemical environment of the follicle, potentially stimulating hair growth and regeneration.

Biophysics and the Future of Biological Research

This research highlights the growing importance of biophysics in understanding fundamental biological processes. It demonstrates how microscopic mechanical forces can significantly influence the growth and behavior of structures within the human body.

Source: Queen Mary University of London, ScienceDaily, Science News Today, Nature Communications