There are many reasons: the disease has a certain genetic susceptibility, but it is not a hereditary disease; it can be induced under the influence of environmental factors: 1, countries far from the equator, such as: the United States, Scandinavia, Canada, the incidence rate is significantly higher, and Africa and other countries near the equator have a low incidence rate. 2, viral infections (eg: often after the onset of colds); 3, bacterial infections; 4, changes in the level of sex hormones (such as before and after pregnancy); 5, industrialization, pollution, occupational exposure to organic solvents, contact with toxic chemicals such as pesticides, etc.; 6, diet, as well as changes in breastfeeding habits; 7, there are also bad habits, such as smoking, staying up all night, and so on, factors can be triggered by the onset of the disease.