 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 follows by shorter <unk> ( transition ) and <unk> ( resting ) periods . Between 85 % and 90 % of the hair strands are in anagen at any given time . The <unk> 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 . 
