Excessive or abnormal hair loss is known as alopecia, and there are several kinds. What all hair loss has in common, whether it's in men or women, is a symptom of something that's gone wrong in your body. Your hair will remain on your head where it belongs unless hormone imbalance, disease, or some other condition occurs. That condition may be as simple as having a gene that makes you susceptible to male or female pattern baldness or one of the forms of alopecia areata, or it may be as complex as a whole host of diseases.
Fortunately, hair loss can be a symptom of a short-term event such as stress, pregnancy, disease, or medication, which can all alter hair's growth and shedding phases. In these situations, hair will grow back when the event has passed. Once the cause of the loss is addressed, hairs go back to their random pattern of growth and shedding, and your problem stops.
The first two types of hair loss in women are associated with dihydrotestosterone (DHT), a derivative of the male hormone, testosterone.
The majority of women with androgenetic - also called androgenic - alopecia have diffuse thinning on all areas of the scalp. (Men rarely have diffuse thinning but instead have more distinct patterns of baldness.) Some women have a combination of two pattern types.
Androgenic alopecia in women is due to the action of androgens, male hormones that are typically present in only small amounts. Androgenic alopecia can be caused by a variety of factors tied to the actions of hormones, including some ovarian cysts, taking high androgen index birth control pills, pregnancy, and menopause.
Just as in men, the hormone DHT appears to be at least partially to blame for the miniaturization of hair follicles in women suffering with female pattern baldness. Heredity plays a major factor in the disease.
When your body goes through something traumatic like child birth, malnutrition, a severe infection, major surgery, or extreme stress, it can impact your hair. Many of the 90% or so of hairs in the growing (anagen) or transitional (catagen) phases can actually shift all at once into the resting (telogen) phase.