Taken out of my Anatomy & Physiology textbook. A little summary of hair structure & growth/loss.
Hair and Nails are composed of mostly Hard Keratin (dead
The only living cells of a hair are in and near the bulb.
The bulb grows around a bud of vascular connective tissue which provides the
hair with its sole source of nutrition.
Hair Cycle: anagen, catagen, and telogen
Anagen stage: Growing
Phase, 6-8 years. At any given time, 90% of the scalp follicles are in the
anagen stage. Stem cells multiply and follicle grows deeper into skin. New hair grows up the follicle, alongside an
old “club” hair left from the previous cycle.
Club hair is the hair that falls out when we brush.
Catagen stage: Degenerative
phase, 2-3 weeks. Hair growth ceases, hair bulb keratinizes and forms club
hair. Lower follicle degenerates.
Telogen stage: Resting phase, 1-2 months. Club hair falls
We lose about 50-100 scalp hairs daily.
Scalp hair grows at a rate of about 1mm per 3 days (10-18
cm/yr) in anagen phase.
Hair grows fastest from adolescence until the 40s. After
that, an increasing percentage of follicles are in the catagen and telogen
phase rather than the growing anagen phase.