Pathophysiology of Hair Loss

Hair is one of the major determinants of beauty. Everybody’s dream is to have a nice head of healthy hair. Hair loss is a very distressing experience, especially for women. A person normally loses a certain amount of hair every day. This is not pathological. Hair loss becomes excessive when there is an underlying disease, which requires further investigation and management.

As mentioned earlier, there are two types of hair loss: pathological and non-pathological. To differentiate and identify pathological hair loss, one should have a clear knowledge regarding non-pathological hair loss. Each and every hair in human scalp has a life cycle. The hair falls off once the life cycle is completed. This is not pathological.

The life cycle of a hair is divided into three phases. They are anagen, catagen and telogen. Anagen phase of the hair is where the cells in the root of the hair grow and produce new hair. As a result the hair increases in length. Researchers have found that the hair grows about 1 cm every 28 days. The next phase of hair growth is the catagen phase. This is the transitional phase where the hair stops growing. The phase lasts for about three weeks. Formation of club hair occurs at this phase. The telogen phase is the resting phase of a hair. This is where the hair has completely stopped growing. Six to eight percent of hair in the scalp is in this phase of life cycle. Normally, 25-100 hairs in the telogen phase are shed every day.

Pathological hair loss occurs as a result of insult to the hair follicles. There are many physical, chemical and biological insults that result in excessive hair loss. Each hair is attached to the scalp through the hair follicle. The hair follicle is responsible for hair growth. Therefore, anything that affects the hair follicles may cause premature loss of hair.

There can be direct insult to the hair follicles. For example, in diseases such as Graves’ disease, there are circulating antibodies which can attack the hair follicles. Once these antibodies attack the hair follicle, the follicle loses its function. As a result, the hair follicle dies, and the whole hair is shed. Excessive amounts of circulating testosterone levels also cause excessive hair loss by interfering with the normal function of the hair follicle. For the hair follicle to function well, it should receive adequate amounts of nutrients. Therefore, there should be a good blood supply to the scalp. Anything that impairs scalp blood supply can cause hair loss.

As described above, hair loss can be pathological or non-pathological. Identifying the pathological causes of hair loss is very important to treat the underlying condition. Some people identify physiological hair loss as a pathological condition. Those people should be educated regarding the physiology of hair loss and reassured.