Female pattern hair loss or genetic alopecia is the most common reason of hair loss in women and it is more common than it is thought to be. 25% of the women at the ages of 35-40, 50% of the women at the ages above 40 suffer from hair loss. 20% of the women with hair loss have a positive relative who suffered/is suffering from hair loss. Other reasons of hair loss are: Hypo- and hyper-tiroidism (hair loss may be one of the early signs of thyroid dysfunction, and hair loss stops after treatment); polycystic ovarian syndrome (an inherited ovarian disease, seen in 10% of the women during adulthood); pregnancy-related hormonal changes (temporary hair loss which can be seen during pregnancy stops after birth)..    The reason of the hair loss may be external factors, connective tissue disorders such as stress, anemia, lupus, medications, hormonal and seasonal changes, nutritional problems, severe diets, bulimia, protein/calorie deficiency, zinc and essential amino-acid deficiency, mal-absorption (intestinal and digestive problems), A-vitamin excess, general anesthesia, affective mood disorders. So you have to have a full exam with an hair surgeon, internalist and/or endocrinologist to find out any reason for hair loss.