The normal growth rate of scalp hair is one-fourth to one-half inch per month. Hair growth has a cyclic pattern that can be affected by a number of genetic, disease, medication or other factors to cause hair loss.

Hair is formed in the hair follicle and grows out of the follicle in a continuous cyclic pattern of growth and rest. There are three phases in the hair growth cycle:

• Anagen—growth phase, 2 to 8 years;
• Catagen—degeneration phase, 2 to 4 weeks; and,
• Telogen—resting phase, 2 to 4 months.

During anagen the follicle actively grows hair.

During catagen the follicle is almost entirely degraded.

During telogen the follicle rests prior to re-initiation of an anagen phase and the growth of a new hair shaft>

As the new hair shaft emerges it pushes out the prior “dead” hair shaft, and the old hair is shed. About 50 to 100 telogen hairs are normally shed every day; these are the hairs we find in our comb, brush and shower drain. About 10 percent of scalp hair follicles are normally in telogen phase at any given time if the scalp is healthy and not affected by any condition that causes hair loss.

Excerpts copied from International Society of Hair Restoration Surgery, www.ISHRS.org, © 2004.