What causes alopecia?

Alopecia is classified into four types: androgenic alopecia, alopecia pityroides, seborrheic alopecia, and alopecia areata. More than ninety percent of hair loss is due to androgenic alopecia, and about thirty percent of men aged 20 to 60 have androgenic alopecia. What we call “hair loss” is not caused by loss of hair follicles. Rather, it is because the growth period (anagen phase) has been gradually shortened and hair on the frontal region and top of head has become too soft and weak even though hair on these region is originally firm and strong. The reason why hair on top of head looks lost is not because these hairs actually have been lost but because top hair has become so thin that it is almost invisible.

Androgenic alopecia (AGA)

　People with this type of alopecia have too soft hair. AGA is hereditary in general. You might worry about your hair getting thin if your father also had such a hair problem. Steroidal testosterone, most of which is made in testis, combined with a kind of enzyme called 5 – α reductase in the roots of hair, results in powerful testosterone, namely, dihydrotesosterone (DHT). DHT is thought to cause AGA. When DHT, combined with proteins that function as a receptor of DHT, operates on sebaceous glands on the scalp, excessive sebum is secreted, which prevents hair growth. This shortens the cycle of hair growth, and thus, new hair remains to be fluff, stops growing, and finally falls out. Because proteins that work as a DHT receptor gathers especially on frontal region and top of head, hairs on these regions are most likely to fall out.

Alopecia pityroides

　This type of alopecia is due to excessive dandruff. Everyone has more or less dandruff on his or her scalp, but, if he or she has scalp keratosis, excessive sebum, mixed with dandruff, covers pores on the scalp. This damages cells that produce new hairs, resulting in hair loss. Excessive dandruff can result from poor diet and the use of shampoo that does not suit one’s constitution. In some cases, this type of alopecia leads to loss of hairs on only some regions of head, but in others, it causes hair loss all over the head.

Seborrheic alopecia

　This type of alopecia is due to excessive sebum and/or oily dandruff, which cover the root of hair. Oxidized sebum damages cells that produce new hair. It also makes it difficult for hair to “stick to” scalp, resulting in hair loss. Sebaceous secretion is related to life styles, eating habit, and individual constitution.

Alopecia areata (Circular loss of hair)

　This type of alopecia is characterized by one or several bald spots that vary in size from a grain of rice to a quarter coin. These bald spots sometimes grow together, and in the worst case, hair all over the head falls out. The reason for this type of alopecia is because too much stress prevents blood flow and nerve functions, which, in turn, hinders cells from producing new hair. This alopecia is also due to too sensitive physiological responses.