Anagenphase

Anagen phase, or growth phase, is the first stage of the hair cycle during which the hair follicle is actively producing hair. In this phase the hair matrix cells at the base of the follicle divide rapidly, lengthening the hair shaft and contributing pigment as melanocytes transfer pigment to the growing hair. The anagen phase is followed by the catagen (transition) and telogen (resting) phases, and in some models an exogen phase refers to the shedding of hair.

Duration and characteristics vary by body site and individual. On the scalp, the anagen phase can last several years, typically ranging from about 2 to 6 years and sometimes longer. The length of the anagen phase largely determines how long hair can grow before a transition to catagen occurs. At any given time, the majority of scalp hairs are in anagen; estimates commonly place this around 85–90% in healthy adults.

Growth rate during anagen is relatively steady, with scalp hair commonly increasing about 1 centimeter per month, though rates can differ among individuals. The phase is influenced by genetic factors, hormonal signals (notably androgens in certain conditions), nutritional status, age, and overall health. Conditions that shorten or disrupt anagen, such as androgenetic alopecia or systemic illness, can lead to shorter hair length and slower apparent growth. Chemotherapy and other cytotoxic treatments may induce anagen effluvium by impairing rapidly dividing matrix cells, causing rapid shedding of actively growing hair.