Hair Cycle

Hair Cycle

• Each hair follicle undergoes repeated cycles of active growth and of rest.  The relative duration of phases of cycle varies with the age of the individual and the region of the body, and can be modified by a variety of physiological and pathological factors.  

• Anagen: active growth phase - 1000 days on the scalp, 28 days on eyebrows
• Catagen: phase of involution - complete in few days
• Telogen: resting phase - clubbed hair, duration 100 days

• Ratio of anagen/telogen varies according to body location: On the scalp it is 9/1; eyebrow 1/9
• Population of scalp follicles: 100,000. Blondes have more and redheads have less. 
• Average shed: 100/day  

Growth rate

• 0.21 mm/day - female thigh
• 0.38 mm/day - male chin
• 0.5 mm/day - crown of scalp

Shaving has no effect on the rate of hair growth.

• Cross-sectional shape determines texture of the hair.  There are ethnic differences:
  • Straight: round (Oriental)
  • Wavy: oval (Caucasian)
  • Curly/kinky: flat (Afro-Canadian)