The most common cause of hair loss in both men and women is due to androgenetic alopecia. In this case, genetically predisposed individuals are particularly sensitive to a testosterone derivative called dihydrotestesterone, or DHT. This hormone retards hair growth and metabolism, slowing causing progressively more hair to die out.
Other causes of hair loss include hormonal conditions (pregnancy, thyroid disorder, polycystic ovary, menopause), anemia, autoimmune disorder, quick weight loss, medications, stress, chemicals, trauma, and local skin diseases.