Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 50 3 2021 02 26 431 437 Yue HE Department of Respiratory and Critical Care Medicine, The Affiliated Hospital of Qingdao University, Qingdao, Shandong, China Jian SUN Department of Respiratory and Critical Care Medicine, The Affiliated Hospital of Qingdao University, Qingdao, Shandong, China Xiaoqian DING Department of Respiratory and Critical Care Medicine, The Affiliated Hospital of Qingdao University, Qingdao, Shandong, China Qiang WANG Department of Respiratory and Critical Care Medicine, The Affiliated Hospital of Qingdao University, Qingdao, Shandong, China 2020 09 30 2020 10 14 At present, COVID-19 continues to spread around the world. People are generally susceptible to SARS-CoV-2. The elderly, serious chronic underlying diseases, high-risk pregnancy, severe obesity and other factors are related to the progression of COVID-19 to severe, critical illness, and even death caused by deterioration of the disease. The relationship between smoking and COVID-19 seems to be controversial. The smoking rate of hospitalized COVID-19 patients is significantly lower than that of the general population. Therefore, smoking can reduce COVID-19 infection and protect the respiratory tract. Subsequently, many scholars have carried out research on this, thinking that this is a wrong and misleading conclusion. According to WHO, smoking is significantly related to the severity of COVID-19, which is one of the important risk factors for the deterioration and poor prognosis of COVID-19. This article reviews the mechanism of smoking increasing the risk of COVID-19 infection. https://ijph.tums.ac.ir/index.php/ijph/article/view/22376 https://ijph.tums.ac.ir/index.php/ijph/article/download/22376/7152