There are many causes for hair loss in men or women. However, in the overwhelming majority of males with hair loss, the cause is hereditary androgenetic alopecia, more commonly known as “male pattern baldness.” The presence of the hormone, dihydrotestosterone (DHT), in a genetically susceptible man, is necessary for this problem to occur. Similarly, for females most patients presenting with hair loss have hereditary female pattern hair loss. This condition is still being researched, but the hormone influences on hereditary hair loss in females may be different from those in males. Some of the less common causes of hair loss, which are reversible with treatment, include thyroid disease, iron deficiency, high fever, surgery or general anesthesia, “crash diets,” childbirth, and certain medications. There are also certain dermatologic scalp disorders that can result in temporary or permanent hair loss, such as lupus, lichen planopilaris, and alopecia areata.
Many myths abound regarding this topic; hair loss is NOT caused by poor circulation, clogged hair follicles, frequent shampooing, the wearing of hats or helmets, or the presence of mites. It is also important to remember that most adults lose approximately 75–125 hairs from their scalps every day due to the natural process whereby some hairs go into a dormant state (telogen), and others come out of this state and begin to sprout a new hair (anagen). As long as the process remains balanced, the number of hairs on the scalp remains constant. One other minor factor in hair loss is stress, which is thought to accelerate already genetically programmed hair loss. However, it probably does not cause hair loss by itself without the necessary genes and hormones.
The tendency for male and female pattern hair loss is genetically inherited from either side of the family and begins to develop after puberty. Hair on the scalp that is genetically susceptible to androgenetic alopecia (generally the front and top of the scalp), starts to shrink in its shaft diameter and potential length during each 3 to 5 year “life cycle,” until it eventually disappears. The hair on the back and sides of most men’s scalps is usually genetically “permanent” hair, which is destined to remain for that man’s lifetime.