The causes of low percentage of lymphocytes may be exposure to radiation, drug-induced, immunodeficiency virus infection, etc. The main hazards are caused by the primary disease or causative factors, such as prolonged exposure to radiation can cause leukemia, thyroid cancer, etc., and the progression of AIDS can be life-threatening. 1. Exposure to radiation: the longer the exposure time, the greater the harm, not only can kill the normal cells of the human body, but also can cause cell mutation, inhibit bone marrow hematopoiesis, thus inducing a series of diseases such as aplastic anemia, acute leukemia, etc., and can be due to the progression of the disease and endangered life. 2. Drug-induced: such as long-term application of adrenocorticotropic hormone or pro-adrenocorticotropic hormone, which can reduce the percentage of lymphocytes in the human body. Long-term use of such drugs can inhibit protein synthesis, which can cause osteoporosis and even fractures. 3. Human immunodeficiency virus infection: destroys lymphocytes, leading to decreased immunity and high mortality in severe cases. In addition to the above hazards, low percentage of lymphocytes will also cause a decline in immunity, which will also lead to recurrent infections and prolonged treatment of other diseases. It is recommended to take standardized treatment under the guidance of a physician as soon as possible in order to reduce the adverse effects of the disease.