Low cd4/cd8 may be caused by immunodeficiency diseases, malignant tumors, primary cellular immunodeficiency diseases or combined immunodeficiency diseases. 1. Autoimmune diseases: cd4/cd8 is the ratio of T-lymphocyte subpopulation in the body. Lymphocyte is an important cell in the body’s immune regulation, which mainly plays the role of regulating the immune function in the body, therefore, when there are autoimmune diseases such as systemic lupus erythematosus in the body, the index will be low. 2. Malignant tumor: the immunity of the body and the development of tumor have certain correlation, the immunity function of the body of patients with malignant tumor is poor, so the phenomenon of low cd4/cd8 will occur. 3. Primary cellular immunodeficiency disease or combined immunodeficiency disease: when the body appears pediatric vesicular eczema syndrome, severe combined immunodeficiency disease, DiGeorg syndrome and so on will cause cd4/cd8 low phenomenon, the reason is that the above diseases will lead to the body to appear immunodeficiency. When cd4/cd8 is low, it is recommended to go to the hospital for examination to clarify the cause of the disease and timely treatment under the guidance of physicians.