Secondhand smoke may cause leukemia. A survey and research conducted by the Department of Children’s Hematology and Oncology of a hospital showed that more than 60% of families with leukemia are contaminated by secondhand smoke. In recent years, the incidence of childhood leukemia in China is on the rise, the number of leukemia cases ranked in the top four, the toxins produced by secondhand smoke on leukemia is becoming increasingly serious. Secondhand smoke contains dozens of carcinogenic substances, such as heavy metals, nitrosamines and polycyclic aromatic hydrocarbons, etc., which can interfere with the normal cell division of the human body and destroy the immune function of the body, thus causing cancer. Therefore, long-term second-hand smoke will increase the prevalence of leukemia, especially for infants and children with weaker resistance is more dangerous. It is recommended to stay away from second-hand smoke and take good ventilation measures. Diagnosis and treatment should be carried out under the guidance of a physician.