Male and Female hormones (androgens) and heredity (genetics) determine male / female pattern hair loss. Androgentic Alopecia (Pattern Hair Loss) is the most common type of hair loss in men and women. By the age of 50, approximately 50% of men will experience this type of hair loss to some degree.

Men and Women also experience hair loss from other causes, many which are temporary. These include: the stress of an illness or major surgery, medicines such as those used in chemotherapy, blood thinners, antidepressants, excessive amounts of vitamin A and diseases such as diabetes.

Each hair on your scalp grows continuously for approximately 2 to 4 years, stops growing for 2 to 4 months, and then falls out. In its place a new healthy hair begins to grow, and the cycle is repeated. The hairs on your head are always in different stages of this cycle; so it is normal to lose scalp hair every day. Normally, an average of up to 100 hairs is lost per day.

When men and women exhibit pattern hair loss, the normal hair growth cycle is disrupted resulting in an acceleration of daily hair loss without the replacement of new hairs. 

An enzyme in your body known as 5 alpha-reductase converts the hormone testosterone into another hormone known as dihydrotestosterone (DHT). Men and women with pattern hair loss have increased levels of DHT in the scalp. DHT contributes to a shortening of the growth phase and thinning of the hair. This condition begins to occur in men and women in there twenties and becomes even more common as one ages.