For decades, biology textbooks have taught that human hair grows because cells at the base of the hair follicle divide and push up the hair shaft. But new research suggests the explanation is incomplete. Scientists have now found evidence that hair growth is stimulated by hidden pulling forces generated by the movement of cells within the hair follicle.
The discovery challenges long-held ideas about how hair grows and could prompt researchers to rethink everything from hair loss treatments to regenerative medicine.
The findings, by researchers from L’Oréal Research & Innovation and Queen Mary University of London, were published in the journal nature communications.
inside the hair follicle
Hair follicles are complex structures embedded within the skin that produce and support each hair. At the base of the hair follicle is the hair bulb, where cells rapidly divide to produce new hair. Scientists have traditionally believed that these newly formed cells act like a conveyor belt, pushing older cells upwards to generate hair from the scalp.
To investigate whether this explanation tells the whole story, researchers used advanced 3D live imaging technology to observe live human hair follicles maintained in laboratory culture. Unlike traditional microscopy, which only captures static images, this approach allows scientists to observe the movement and interactions of individual cells in real time.
The research team focused on the outer root sheath, a layer of tissue that surrounds the growing hair shaft. Remarkably, they observed that cells within this layer were moving downward in a coordinated spiral pattern. What’s even more interesting is that this movement occurred in the same area where the force pulling the hair upwards appears to be occurring.
hidden cellular motor
Dr. Inés Sequeira, Reader in Oral and Skin Biology at Queen Mary University and one of the study’s lead authors, said:
“Our results reveal interesting dynamics inside the hair follicle. For decades, it was thought that hair was pushed out by dividing cells within the hair bulb. Instead, we found that the hair is actively pulled upwards by the surrounding tissue, which acts almost like a tiny motor.”
This finding suggests that hair growth relies not only on the generation of new cells, but also on mechanical forces generated by the coordinated movement of cells within the hair follicle itself.
Surprising results that challenge conventional thinking
To test their theory, the researchers performed a series of experiments designed to separate the effects of cell division from those of cell movement.
First, they blocked cell division within the follicle. If the conventional explanation is completely correct, hair growth should slow down dramatically or stop altogether. Instead, the hair follicles continued to produce hair at about the same rate as before.
Next, the research team focused on actin, a protein found in cells throughout the body. Actin plays a critical role in helping cells move, change shape, and generate force.
When researchers interfered with actin activity, the results were dramatic. Hair growth rates were reduced by more than 80%, indicating that cell movement and force generation are important parts of the growth process.
Computer simulations confirmed these findings. The model showed that the coordinated movement of cells in the outer layer of the hair follicle produces pulling forces strong enough to explain the observed hair shaft movements.
Capturing hair growth in real time
Dr. Nicolas Tissot, lead author of the study from L’Oréal’s Advanced Research Team, emphasized the importance of the new imaging approach:
“We are using a novel imaging technique that enables 3D time-lapse microscopy in real time. While static images provide just an isolated snapshot, 3D time-lapse microscopy is essential to truly unravel the complex and dynamic biological processes within the hair follicle, revealing important cell dynamics, migration patterns, and cell division rates that are otherwise impossible to infer from individual observations. This approach has made it possible to model locally generated forces.”
By tracking living cells over long periods of time, researchers were able to observe biological processes that remained hidden using traditional methods.
New possibilities for hair loss research
The findings may have important implications for understanding hair loss and developing new treatments.
Dr. Thomas Bornschlaegl, another lead author from L’Oréal’s advanced research team, explained:
“This reveals that hair growth is not driven solely by cell division; instead, the outer root sheath actively pulls the hair upwards. This new perspective on hair follicle mechanics opens new opportunities for hair disease research, drug testing, and advances in tissue engineering and regenerative medicine.”
Scientists are increasingly recognizing that biological tissues are shaped not only by genes and chemical signals but also by physical forces. Understanding how these forces influence hair growth may help researchers design future treatments that target both the biochemical environment of the hair follicle and its mechanical behavior.
Although this experiment was performed on human hair follicles grown in laboratory cultures rather than directly on humans, the discovery provides valuable new insight into how hair follicles work.
The researchers also believe their imaging technology could become a powerful tool for evaluating potential hair loss treatments, allowing them to observe in real time how living hair follicles respond to different drugs and treatments.
A new role for biophysics in everyday biology
The study highlights the growing importance of biophysics, a field that explores how physical forces affect living systems, beyond the study of hair.
This result suggests that microscopic mechanical forces may play a major role in the formation of organs and tissues throughout the body. In the case of hair growth, what once seemed like a simple process may actually rely on highly coordinated cellular machinery operating behind the scenes.
If confirmed in future studies, this newly discovered mechanism could change the way scientists understand one of the most well-known biological processes in everyday life.
