Plucking-Induced Hair Regeneration Is a Population-Based Behavior that Depends on the Density and Distribution of Plucked-Hair Follicles within the Unplucked Follicle Population (Credit: “Enhance hair growth via plucking” [D2014-0054], University of Southern California).

Plucking-Induced Hair Regeneration Is a Population-Based Behavior that Depends on the Density and Distribution of Plucked-Hair Follicles within the Unplucked Follicle Population (Credit: “Enhance hair growth via plucking” [D2014-0054], University of Southern California).

(A and B) Plucking 200 hairs from a circular 2.4mm in diameter area (100% plucking) leads to hair regeneration 12 days later. Plucking 200 hairs in a 12 mm diameter area (100 mm2 area; low density plucking) fails to induce follicle regeneration even 30 days later.

(C) Plucking induces regeneration of all follicles (the 200 plucked and 600 unplucked) within the plucked area (red circle, 5 mm in diameter). Unplucked follicles (400 HFs in total) outside the plucked area boundary then regenerate due to hair wave propagation (blue circle).

(D) High power view showing unplucked follicle regeneration: the old gray club hair (yellow) is pushed out by the regenerating black anagen hair (red).

(E) In this schematic drawing, gray dots represent telogen HFs. Black lines encircle exemplary plucked regions. Plucked follicles (purple dots). Regenerating plucked HFs (green dots). Regenerating unplucked HFs (tan dots).

(F) Plot showing the hair regeneration response versus the size of the plucked field. For all different field sizes, 200 hairs are plucked evenly dispersed throughout the field. A regenerative response is observed when 200 hairs are plucked at a density above a threshold (10 hairs/mm2), which corresponds to plucking 200 hairs from a 5-mm diameter circular surface area (red line). Three responses represented by different colors (gray, tan, green), are observed (please see text for explanation). The quorum sensing zone is highlighted in orange.

(Credit: “Enhance hair growth via plucking” [D2014-0054], University of Southern California).