Human hair growth
The three stages of hair growth are the anagen, catagen, and telogen phases. Each strand of hair on the human body is at its own stage of development. Once the cycle is complete, it restarts and a new strand of hair begins to form. The rate or speed of hair growth is about 1.25 centimetres or 0.5 inches per month, or about 15 centimetres or 6 inches per year.
Long hair
The maximum terminal hair length depends on the length of the anagen (period of hair growth) for the individual. Waist-length hair or longer is only possible to reach for people with long anagen. The anagen lasts between 2 and 7 years, for some individuals even longer, and is followed by shorter catagen (transition) and telogen (resting) periods. At any given time, about 85% of hair strands are in anagen. The fibroblast growth factor 5 (FGF5) gene affects the hair cycle in mammals including humans; blocking FGF5 in the human scalp (by applying a herbal extract that blocked FGF5) extends the hair cycle, resulting in less hair fall and increased hair growth.