Most hair loss is caused by pattern baldness.
While the actual cause is not known, the most commonly accepted theory is that male pattern baldness is inherited. There also seems to be a link between the oil glands of the scalp, DHT and cholesterol. In 1986, University of Miami scientists reported a link between enlarged overactive oil glands of the scalp and over production of male hormones in cases with pattern baldness. This supports another theory, that in addition to the inherited tendencies, the oil and sweat glands of the scalp tend to overproduce. These excess fluids mix together with other complex chemicals in the scalp, such as cholesterol and DHT, and interfere with hair regrowth because they tie up molecular binding sites that then send signals to your follicles to gradually shut down hair growth.