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).
Underarm hair
Underarm hair, as human body hair, normally starts to appear at the beginning of puberty, with growth usually completed by the end of the teenage years.
Axillary hair goes through 4 stages of development, driven by weak androgens produced by the adrenal in males and females during adrenarche, and testosterone from the testicle in males during puberty. Like Tanner Staging for pubic hair, axillary hair can be staged according to the staging system, named for Pediatric Endocrinologist, , as follows:
Staging a patient's axillary hair will allow the physician to track the child's development longitudinally.