Normally, about 10 percent of the hair on your head is resting (not growing). After a few months, the resting hair falls out and new hair begins to grow in its place. The growing phase can last from 2 to 6 years. While in the growing phase, hair will gain approximately 1 centimeter a month. It is normal to experience hair loss every day as part of this normal resting/growing cycle. Some people experience excessive hair loss from a variety of causes.
The cause of hair loss is multi-variable. Most people erroneously believe that hair loss is caused by things like bad circulation, stress, sweat and dirt on the scalp, or wearing hats. With the exception of stress, none of these factors has been proven as a cause of hair loss. Stress is also not very likely unless you have undergone extreme physical or psychological torture. This hair loss is also temporary.
The real cause of hair loss lies with hormonal problems. Hair loss occurs when male or female hormones (androgens and estrogens) are out of balance. An imbalance of hormones is usually a genetic trait that as of yet, cannot be cured. Male and female-pattern baldness is the most common form of hair loss. This is caused by a hormone called DHT, a naturally occurring hormone that helps in sexual development. After puberty, an increase in DHT causes an increase in binding at hair follicle protein receptor sites which throws the process of healthy hair growth off.
Other causes of hair loss may be medicine. Blood-thinners, medicines used in chemotherapy, an excess of vitamin A, birth control pills, and antidepressants have all been shown to promote hair loss in certain people. Infections of the scalp can cause hair loss as well as certain diseases like lupus and diabetes.