There is a patch on the head with no hair

Some people lose hair for various reasons, and hair loss is normal. But for some people, there will be an area where hair cannot grow after they lose their hair. What is the reason for a hairless area on the head? It should be alopecia areata. Alopecia areata is a sudden onset of localized patchy hair loss. Its characteristics are that the scalp at the lesion site is normal, there is no inflammation or subjective symptoms. It is often discovered inadvertently. There are round or oval hair loss patches on the head. The hair at the edge of the bald area is loose and easy to pull out. The course of alopecia areata is slow and can last for months to years. The disease can resolve on its own but often recurs. In about 5-10% of alopecia areata cases, all hair falls out within a few days or months, becoming total baldness.

1. About 10% to 20% of cases of genetic allergies have a family history. There are reports of monozygotic twins suffering from alopecia areata in the same area at the same time, and there are also reports of four generations of a family suffering from alopecia areata. It is believed to be a genetic defect disease. It can be seen from the accumulated clinical cases that people with genetic allergic constitution are prone to alopecia areata. According to statistics in the United States, 18% of children with alopecia areata have eczema or asthma, or both; about 9% of adults have alopecia areata; and the number of children with alopecia totalis is even higher, accounting for 23%. According to statistics from Japan, 10% of alopecia areata patients have genetic allergies, while the figure in the Netherlands is as high as 52.4%. However, the basis for establishing genetic allergic constitution in the Netherlands is to include those with positive skin tests and a family history of genetic allergies. Therefore, different countries and regions have different diagnostic standards for genetic allergies, and the data cannot be compared. A study on alopecia areata and human leukocyte antigen conducted by Chen Shengqiang in China showed that the frequency of HLA-A9 antigen in patients with alopecia areata (16.67%) was significantly lower than that in normal people (32.65%), which supports the genetic allergic factor of alopecia areata from an experimental perspective.

2. The rate of patients with autoimmune alopecia areata suffering from some autoimmune diseases is higher than that of the normal population. For example, those with thyroid disease account for 0-8%; those with vitiligo account for 4% (only 1% of normal people). However, research reports on autoantibodies in patients with alopecia areata are inconsistent, with some saying they exist and others saying they have not been found. A study on T cell subsets and β2 microglobulin by Zhang Xinjiang in China suggested that patients with alopecia areata have T cell network disorders and humoral immune disorders.

3. Down syndrome The incidence of alopecia areata increases in Down syndrome, often alopecia totalis or alopecia universalis. The presence of autoantibodies was significantly increased in these patients.

It is not certain that alopecia areata is an autoimmune disease, but the fact that it may be accompanied by autoimmune diseases and be temporarily effective in response to corticosteroids suggests that it tends to be based on the autoimmune theory.

After long-term investigation and research, Ikeda of Japan believes that alopecia areata can be divided into four types, each with different onset ages, clinical manifestations and prevention.

Type I, hereditary allergic (10%): early onset, long course, 75% develop into total alopecia.

Type II, autoimmune (5%): usually develops after age 40.

Type III, prehypertensive (4%): Onset in young adults, one or both parents is a hypertensive patient. The disease progresses rapidly, with alopecia totalis occurring in 39%.

Type IV, common type (83%): does not belong to types I to III. The disease occurs in late childhood or young people, and the total course of the disease is usually within 3 years. A single alopecia areata can grow hair within 6 months. 6% develop total alopecia.