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Structure of hair follicle. (A) A human scalp hair follicle (anagen VI): the permanent (infundibulum, isthmus) and anagen associated (suprabulbar and bulbar area) components of the hair follicle. (B) Schematic diagram of the concentric layers of the hair follicle bulb, including hair shaft, IRS, outer root sheath, and connective tissue sheath. IRS, inner root sheath.
