Hair care
Scalp hair grows, on average, at a rate of about 1.25 centimeters per month, and shampoos or vitamins have not been shown to noticeably change this rate. Hair growth rate also depends upon what phase in the cycle of hair growth one is actually in; there are three phases. The speed of hair growth varies based upon genetics, gender, age, hormones, and may be reduced by nutrient deficiency (i.e., anorexia, anemia, zinc deficiency) and hormonal fluctuations (i.e., menopause, polycystic ovaries, thyroid disease).
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.