Hair doesn’t grow the way scientists have always assumed

Curious minds might assume that hair science was settled long ago. After all, countless guides describe how hair grows, renews itself, and eventually falls out.

But new research using advanced follicle cultures reveals a far more dynamic world beneath each strand.

Inside what once seemed like a simple tiny tube, motion, force, and finely tuned organization are constantly at work.

Live follicle imaging now exposes a choreography of coordinated movements and shifting pathways – inviting a fresh perspective on how hair truly grows.

How hair grows upward

Older models portrayed hair growth as a simple upward push from rapidly dividing cells beneath the emerging fiber.

However, the live-culture imaging reveals something very different: spiraling movements, sliding cell zones, and an upward pull created by coordinated downward shifts in the outer layers of the follicle.

The imaging shows outer layers curling downward within narrow shells. Upward motion appears linked to spiral descent rather than crowding under a shaft.

“Our results reveal a fascinating choreography inside the hair follicle. For decades, it was assumed that hair was pushed out by the dividing cells in the hair bulb,” said Dr. Inês Sequeira of the Queen Mary University of London. 

“We found that instead that it’s actively being pulled upwards by surrounding tissue acting almost like a tiny motor.”

Inner layers rising

Inner regions drift upward at differing speeds. Cortex cells climb at a steady rate, while segments of the inner sheath surge much faster.

Motion maps reveal curved trajectories looping around the papilla, echoing patterns long observed in rodent follicles. Cell-division angles align with these local flow paths.

Although matrix pockets near the papilla brim show dense clusters of dividing cells, removing these pockets does not halt upward movement.

Complementary simulations further indicate that cell-division pressure alone cannot account for the measured speeds. Instead, outer layers appear to exert a pulling force that draws the inner zones upward.

Shifting cell motion

Outer layers in culture shift downward in spiral paths, switching direction around cup-shaped bulb regions. Some units move into deeper zones before merging with rising inner layers.

Culture films reveal sliding at junctions where adhesion remains sparse, permitting relative motion between outer and companion regions. Inner layers carry stronger adhesion, guiding unified ascent.

Volume rise occurs in the early stages of upward travel, followed by stable size once maturation begins.

Upward flow continues even once division shuts down under pharmacologic block, revealing independence from mitotic pressure.

Actin helps hair grow

Actin networks inside outer zones form circular arrays above bulb regions and straighter bundles near lower parts. Disruption of actin using cultured samples cuts growth by over 80 percent.

“We use a novel imaging method allowing 3D time lapse microscopy in real-time,” said study lead author Dr. Nicolas Tissot of the L’Oréal Research and Innovation.

“While static images provide mere isolated snapshots, 3D time-lapse microscopy is indispensable for truly unraveling the intricate, dynamic biological processes within the hair follicle.”

Dr. Tissot noted that the imaging revealed crucial cellular kinetics, migratory patterns, and rate of cell divisions that are otherwise impossible to deduce from discrete observations. “This approach made it possible to model the forces generated locally.”

Experiments point to a mechanism in which the outer layers drift downward while actin-driven tension hoists the inner zones upward.

Even when bulb sections are removed, this upward motion persists, confirming that the force originates from pulling rather than pushing.

Mapping the pull system

Simulations using fluid-inspired rules recreate observed speeds only when an active pulling wall moves upward at rates similar to filmed growth.

Models without such a wall fail to match ascent seen in culture films. Upward drift aligns with paths flowing around papilla curves. Inner units glide in onion-like rings, while outer layers descend in paired spirals.

Combined flow satisfies conservation of volume: the inward descent of outer layers balances the outward ascent of inner layers.

New hair growth insights

“This reveals that hair growth is not driven only by cell division – instead, the outer root sheath actively pulls the hair upward,” said study co-author Dr. Thomas Bornschlögl.

“This new view of follicle mechanics opens fresh opportunities for studying hair disorders, testing drugs and advancing tissue engineering and regenerative medicine.”

Culture films offer potent windows for medicine, revealing mechanical cues once invisible under static microscopes.

Together, these mapped flows, forces, and sliding interfaces lay groundwork for new growth therapies and regenerative strategies aimed at repairing damaged follicles.

Emerging imaging methods could further extend filming duration and sharpen tracking of subtle cell populations, from immune sentinels to rare progenitors, opening the way to deeper insight and more precise interventions.

The study is published in the journal Nature Communications.

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