Hair loss typically caused by radiation therapy or chemotherapy. These procedures disrupt the anagen cycle. Hair usually breaks off rather than sheds.

Significant loss of hair during the anagen (growth) phase.

Hairshafts are produced by follicles within the skin in all but few locations viz: palms soles, lips, eyelids, backs of distal phalanges and parts of the external genitalia. Each productive hair follicle provides hairshafts throughout the life of the person. Some follicles may intermittently produce vellus or terminal hairshafts.