For decades, biology textbooks have taught that human hair grows because new cells in the hair root divide and push older cells upward, making the hair shaft extend.
But a new study has turned that idea upside down.
Scientists from L’Oréal Research & Innovation and Queen Mary University of London have found that hair is not pushed out at all—instead, it is pulled upward by a hidden network of moving cells.
The findings, published in Nature Communications, could transform how researchers understand hair growth, hair loss and future treatments.
The team made the discovery using advanced 3D live imaging, a powerful technology that allowed them to track individual cells inside living human hair follicles kept alive in the lab.
This method revealed a surprising pattern: cells in the outer root sheath—a protective layer that wraps around the hair shaft—move in a spiral downward motion.
Yet the force that actually causes the hair to grow upward comes from this very same region.
Dr. Inês Sequeira, a lead author from Queen Mary University of London, explained that the inside of a hair follicle behaves like a “tiny motor.”
Instead of being pushed up from below, the hair is pulled upward by these outer cells as they move and contract. This discovery challenges long-held theories and opens the door to new questions about how hair grows and why it sometimes stops.
To test their theory, the researchers blocked cell division inside the hair follicle. If the old model were correct, hair growth should have stopped.
But remarkably, the hair continued growing almost normally. In contrast, when the team disrupted actin—a protein that helps cells move and generate force—hair growth slowed by more than 80%. This showed that movement and pulling, not cell division alone, are key drivers of hair lengthening.
Computer simulations backed this idea, showing that the observed speeds of hair growth could only be explained if an active pulling force were present.
Dr. Nicolas Tissot from L’Oréal emphasized that the study was made possible by real-time 3D time-lapse microscopy. Unlike traditional static images, this technique captures continuous movement inside the follicle, revealing the complex interplay of cells that previous methods simply could not detect.
Dr. Thomas Bornschlögl, also from L’Oréal, said the findings reshape how scientists think about hair disorders and treatments. Understanding the mechanical forces involved in hair growth may lead to new ways to treat hair loss, test drugs on living follicles and improve regenerative medicine approaches.
The work highlights how biophysics—the study of forces and motion in biology—is becoming essential to understanding living systems. Even something as ordinary as a growing hair turns out to be powered by an intricate and surprising dance of microscopic forces.
