Alopecia classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Classification

Hair Classification

• Anagen: growth phase, lasts 2-3 years (80-90% of follicles at any given time)
• Catagen: involutional phase, lasts 2-3 weeks (1-3% of follicles)
• Telogen: resting phase, lasts 3-4 months (5-10% of follicles)
  • Hair released from shaft and shed at end of telogen new cycle begins
  • Mature root sheath of telogen hair = “club” at proximal end
• Terminal hairs: large shaft diameters, bulbs extend into subcutaneous fat
• Vellus hairs: smaller in caliber and length, less pigmented
• Indeterminate hairs: size/length between that of terminal and vellus hairs