Mapping Cell Dynamics in Human Ex Vivo Hair Follicles Suggests Pulling Mechanism of Hair Growth

Researchers developed a 3D live imaging system to study cell dynamics in human hair follicles during the anagen phase in ex vivo culture. They observed a spiral-like downward movement of outer root sheath cells and an upward flow of cells in the bulb, which aligns with differentiation patterns seen in rodent hair follicles. The study found that cell division rates and orientation in the bulb are linked to the velocities of adjacent upward-moving cell layers, with faster movement associated with higher mitotic rates. By integrating fluid dynamics simulations and experimental manipulation, the researchers propose a model where a pulling force from the outer root sheath aids in hair fiber extrusion.