For men:

Genetics
95% of hair loss is caused by genetic (inherited) makeup. The genes are passed down from either the mother or fathers side of the family. The trait for hairloss can skip generations and may not even affect siblings in the same way. This is true for both men and women.

Alopecia
Alopecia comes in three types. Areata partial - spotty hair loss, totalis - head totally bald and universalis - all hair on body and scalp is lost . Currently it is thought that this condition is an autoimmune disorder with no known cure. Effective treatment is limited to cosmetic, non-surgical solutions.

Chemotherapy
Drug and radiation treatments for cancer patients are designed to poison the cancer cells. In many cases they also poison the hair follicles and result in baldness. This condition is not permanent and most usually upon completion of the treatments the hair will be fully grown back with in a year.

Surgeries, Dieting and Emotional Stress
The human body shuts down production of hair during periods of stress. Occasionally there is a delay between the cause and actually experiencing hair loss. Then another delay from six months to a year before regrowth is seen.

Thyroid Imbalance
Thyroid imbalance and/or anemia can contribute to hair loss. Both can be detected by a simple blood test administered by your health care professional.

Trichotillomania
Trichotillomania (TTM) is an impulse disorder that causes people to pull out the hair from their scalp, eyelashes, eyebrows, or other parts of the body, resulting in noticeable bald patches. It is currently defined as an impulse-control disorder, but there are still questions about how it should be classified. It may seem, at times, to resemble a habit, an addiction, a tic disorder or an obsessive-compulsive disorder. It is estimated to affect one to two percent of the population, or four to eleven million Americans.

Addtional information can be found at:

National Alopeciaareata Foundation

Trichotillomania Learning Center, Inc.