Hormones called androgens, usually testosterone, can cause hair follicles to shrink, causing thinning of hair or eventual hair loss. Reportedly only bone marrow grows faster in our body than hair does. The average scalp contains 100,000-150,000 hair follicles and hairs, with 90% growing and 10% resting at any given time. Hair actually grows in three stages: anagen, catagen, and telogen. The anagen phase is the phase where hair is actively growing, and of course this phase is longer for follicles in the scalp than anywhere else on your body, and lasts longer for women than men. It is natural for follicles to atrophy and hair to fall out, and this is called the catagen phase. This phase is only temporary, and eventually the follicle enters the telogen phase where it is resting. These are the 10% at rest mentioned above. Normal anagen phases last approximately five years, with catagen phases lasting about three weeks, and telogen phases lasting approximately 12 weeks. As you see it is natural to lose some hair. Natural hair loss is considered to be in the range of 100 hairs per day. It is not apparent to most people that hair is actually being lost until more than 50% of a person’s hair is actually lost.

More Hair Facts and Hair Loss Basics

Although both men and women can suffer significant hair loss, over 50% of men will suffer with Male Pattern Baldness (MPB), also known as androgenetic alopecia, at some point in their lives.  The reason behind hair loss is a genetically inherited sensitivity to Dihydrotestosterone (DHT) and 5-alpha-reductase. The enzyme 5-alpha-reductase converts testosterone, a male hormone, to DHT, the substance identified as the end-cause for hair loss.

Most hair loss follows a pattern that has been codified in a table called the Norwood Scale (see figure 1). There are seven patterns of hair identified in the Norwood Scale, Norwood I being a normal head of hair with no visible hair loss, Norwood II showing the hair receding in a wedge-shaped pattern. Norwood III shows the same receding pattern as Norwood II, except the hairline has receded deeper into the frontal area and the temporal area. Type IV on the Norwood Scale indicates a hairline that has receded more dramatically in the frontal region and temporal area. Additionally there is a balding area at the very top center of the head, but there is a bridge of hair remaining between that region and the front. Type V on the Norwood Scale shows that very same bridge between the frontal region and the top center, also called the vertex, beginning to thin. Type VI on the Norwood Scale indicates that the bridge between the frontal region and the vertex has disappeared. Finally, Type VII on the Norwood Scale shows hair receding all the way back to the base of the head and the sides just above the ears. Norwood patterns are determined genetically.