1. Genetic allergy factors About 10% to 20% of cases have a family history. There are reports of monozygotic twins having baldness in the same area at the same time, and there are also reports of a family with baldness in all four generations, which is considered a genetic defective disease. From the accumulated clinical data, it is clear that people with genetic allergies are prone to develop baldness. In the United States, 18% of children with baldness have eczema or asthma, or both; 9% of adults with baldness; and 23% of children with total baldness. In Japan, 10% of patients with baldness have genetic allergies, while in the Netherlands, the percentage is as high as 52.4%. However, the basis for establishing genetic allergies in the Netherlands is to include positive skin tests and a family history of genetic allergies. Therefore, the diagnostic criteria for genetic allergies vary from country to country and region to region, and the data cannot be compared. A study correlating baldness with human leukocyte antigens showed that the frequency of HLA-A9 antigen in patients with baldness (16.67%) was significantly lower than that of normal people (32.65%), proving from an experimental point of view that the onset of baldness is caused by certain genetic allergic factors.
2. Autoimmune factors The rate of autoimmune diseases in patients with baldness 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% in normal people). Studies on autoantibodies in patients with baldness have been reported differently, with some saying they exist and others saying they have not been found. A domestic study on T cell subsets and β2 microglobulin by Zhang Xinjiang suggested the existence of T cell network disorders and humoral immune dysregulation in patients with pemphigus vulgaris.
3.Companionship with other diseases Some patients with baldness are a concomitant manifestation of other diseases, such as hypothyroidism or hyperthyroidism, hypoparathyroidism, anemia, lupus erythematosus, vitiligo, and intestinal parasitic infections.