Results from a study are challenging long-held assumptions about how hair growth is sustained. It turns out that hair does not only grow by being pushed out of the root. Instead, according to advanced imaging and dynamic analysis, it is also pulled upward by coordinated moving cells. The details are discussed in a paper published on 21 November 2025 in Nature Communications.
Not Only Push From Cell Proliferation But Also Mechanical Pulling Action: The Dual Forces That Drive Human Hair Growth
Researchers using advanced imaging uncovered a hidden pulling action inside human hair follicles. This force, driven by actin dynamics in the outer root sheath, proved essential for lifting inner layers upward and sustaining consistent hair fiber growth.
Understanding Further How Human Hair Grows
Tissue morphogenesis, or the process of how tissues form and grow, depends on both biochemical signaling and physical or mechanical factors driven by how cells proliferate, migrate, exert forces, and reorganize. The hair follicle is considered a mini-organ because it provides researchers with insights into homeostasis, stem cell behavior, differentiation, and morphogenesis.
However, most of the aforementioned insights come from studies on rodent hair follicles. Human hair follicles have important differences, such as growth phase, regulation, and structure. Live and dynamic single-cell data from human hair follicles are scarce because studies involving humans are not only technically more challenging but also have ethical considerations.
Scientists from L’Oréal Research & Innovation and Queen Mary University of London designed a study that captured detailed and real-time information on how individual human hair follicle cells move, divide, and generate forces during growth. Their purpose was to dig deeper into the mechanism specific to humans that earlier mouse models could not explain in great detail.
The researchers collected intact human scalp hair follicles and maintained them in controlled laboratory conditions to observe natural growth behavior. They used multiphoton microscopes to capture detailed three-dimensional images over an extended period. This allowed precise tracking of cell movements, divisions, and structural changes within distinct follicle layers.
Imaging was supplemented with computational tools that measured cell speeds and directions throughout the follicle. Tracking software identified individual cells frame by frame, while particle image velocimetry mapped collective tissue flows. These combined approaches provided a clearer picture of dynamic interactions shaping human hair growth in real time.
Mechanical Pulling Action Behind Hair Growth
The central finding showed that human hair growth depended on two coordinated forces working together. To be specific, cells in the hair matrix, near the dermal papilla, multiplied and pushed upward, while outer root sheath cells created a mechanical pulling action. These combined actions produced the steady upward flow needed to form and extend the growing hair.
In simpler terms, earlier knowledge assumed that hair was pushed out by dividing cells in the hair bulb. The finding above challenges this assumption. The imaging and analysis revealed that hair growth involves being actively pulled upwards by surrounding tissue. It is interesting to note that this tissue acts like a small motor that provides the pulling mechanical force.
Hair growth is not simply a result of a push-from-below mechanism from cell proliferation in the hair matrix. The process significantly relies on mechanical pulling from the outer root sheath. This two-component mechanism, proliferation and pulling, is more complex than what simpler animal-based models from previous studies and other investigations assumed.
The findings also change the conceptual understanding of hair follicle biology. It is indeed true that the follicle behaves like a mini-organ, engineered both by dividing cells and mechanical tissue dynamics observed in organ or tissue formation context. The mechanical aspect of hair growth may influence how clinicians think about hair growth regulation and disorders.
FURTHER READING AND REFERENCE
- Tissot, N., Genty, G., Santoprete, R., Baltenneck, F., Thibaut, S., Michelet, J.-F., Sequeira, I., and Bornschlögl, T. 2025. “Mapping Cell Dynamics in Human Ex Vivo Hair Follicles Suggests Pulling Mechanism of Hair Growth.” Nature Communications. 16(1). DOI: 1038/s41467-025-65143-x