Hair loss, or alopecia, has many different causes. Figuring out what is causing your hair loss involves a careful medical history, a review of your hair care practices, an examination of the hair and scalp, blood tests, and sometimes a scalp biopsy.
Everyone is born with a set number of hair follicles, and no new ones are created after birth. Each scalp hair follicle produces an individual hair, called a hair shaft. Hair follicles produce hair shafts in a repeated cycle, each of which lasts several years. After every cycle the hair shaft falls out as the hair follicle produces a new one. Thus, it is normal to lose approximately 100 hairs a day.