About Hair Growth

The human body contains approximately five million hair follicles, while the scalp (prior to any kind of hair loss) contains 100,000 to 150,000 hair follicles. The normal growth rate of scalp hair is one-fourth to one-half inch per month. At our hair replacement center in Rochester, we believe that helping our patients from Buffalo and Syracuse, NY, understand hair growth is important in their understanding of hair loss.

The Normal Hair Growth Cycle

A follicular unit is comprised of the hair shaft and the follicle or root.  The youthful hair follicle has all the requirements (hormone receptors, diverse cell structure and genetic code) to produce the hair on your head. Each hair consists of a series of interconnected proteins known as keratins.

Periods of growth (anagen) last between 2 and 8 years and are followed by a brief period—2 to 4 weeks—in which the hair (not the follicle) begins to separate from the follicle (catagen). Metabolic activity ceases and the resting phase (telogen) begins lasting 2 to 4 months. Shedding of the hair occurs only after the next growth cycle (anagen) begins and a new hair shaft begins to emerge. On average, 100 telogen hairs are shed every day. This is normal hair loss and accounts for the hair loss seen every day in the shower and with hair combing. In a healthy scalp, these hairs will regrow.

The three phases of the cycle are:

1. Anagen = growth phase
2. Catagen = degradation phase
3. Telogen = resting phase

Human hair is produced in a continuous cyclical pattern of growth and rest known as the “hair growth cycle.”

What Hormone Makes Your Hair Grow?

Androgens (testosterone, dihydrotestosterone) are normal hormones present in both men and women.  They are the most important regulators of human hair growth. Androgens must be present for the growth of beard, axillary (underarm), and pubic hair, however they DO NOT cause growth of scalp hair. Dihydrotestosterone is the more potent of the two. In fact, they have the opposite effect on susceptible hairs. A susceptible hair is a hair with a follicle that is genetically coded to die when exposed to an androgen. Most people have a combination of susceptible and non-susceptible hairs. The distribution and ratio of these hairs determines the visible pattern of hair loss. In men, these susceptible follicles are typically present on the top of the scalp, whereas in women they are interspersed throughout the scalp.