Most people never think much about how their hair grows. We notice when it gets longer and needs a haircut, but the process happening inside each hair follicle is hidden beneath the skin.
For many years, biology textbooks have taught a simple explanation. According to this long-accepted idea, new cells in the base of the hair root keep dividing. These new cells then push older cells upward, making the hair shaft grow longer.
Now, a surprising new study suggests that this explanation may not be correct.
Scientists from L’Oréal Research & Innovation and Queen Mary University of London have discovered that human hair does not simply grow because it is pushed upward from below. Instead, hair appears to be pulled upward by a hidden network of moving cells inside the hair follicle. The findings were published in the journal Nature Communications.
A hair follicle is a tiny structure in the skin that produces hair. It contains different layers of cells that work together to create and support the growing hair shaft. Although scientists have studied hair follicles for many years, much of their activity has remained difficult to observe because the structures are so small and dynamic.
To investigate what really happens during hair growth, the research team used advanced three-dimensional live imaging technology.
This method allowed them to keep human hair follicles alive in the laboratory and observe individual cells moving in real time. Unlike traditional methods that provide only still images, this technique captured continuous activity inside living hair follicles.
What the researchers saw surprised them.
Cells in a layer called the outer root sheath, which surrounds and protects the growing hair, were not staying still. Instead, they moved downward in a spiral-like pattern. Even more surprising, these same cells seemed to create the force that caused the hair shaft to move upward.
Dr. Inês Sequeira from Queen Mary University of London, one of the lead authors of the study, said that the inside of a hair follicle acts like a tiny motor. Rather than being pushed from below, the hair is pulled upward by cells in the outer layer as they move and contract.
This discovery challenges ideas that scientists have accepted for decades and raises new questions about how hair growth is controlled.
The researchers then performed additional experiments to test their new theory. They blocked cell division inside the hair follicle. If the traditional explanation were correct, hair growth should have slowed dramatically or stopped completely because new cells would no longer be available to push the hair upward.
But that is not what happened.
Even after cell division was blocked, the hair continued to grow at nearly its normal rate. This suggested that cell division alone could not explain hair growth.
Next, the team focused on actin, a protein that helps cells move and generate force. Actin is found throughout the body and plays an important role in muscle contraction and many other types of cell movement. When the researchers disrupted actin activity inside the hair follicle, hair growth slowed by more than 80 percent.
This result provided strong evidence that movement and pulling forces are essential for hair growth. Computer simulations supported these findings. The models showed that the observed speed of hair growth could only be explained if an active pulling force existed inside the follicle.
Dr. Nicolas Tissot from L’Oréal explained that these discoveries were possible because of real-time three-dimensional time-lapse microscopy. Previous methods could only provide snapshots of the follicle. By observing living tissue continuously, the scientists were able to see complex movements that had remained hidden.
Dr. Thomas Bornschlögl, also from L’Oréal, said the findings may change how researchers think about hair disorders and possible treatments. Hair loss affects millions of people around the world and can have significant emotional and psychological effects.
A better understanding of the mechanical forces that drive hair growth could eventually help scientists develop new ways to treat hair loss, improve drug testing on living hair follicles, and advance regenerative medicine.
The study also highlights the growing importance of biophysics, which examines how physical forces and movement shape living systems.
The research shows that even something as familiar and ordinary as a strand of growing hair depends on a remarkable and complex system of microscopic movements that scientists are only beginning to understand.
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