Smoking is one of the most severe public health problems in the world. According to the WHO Global report on trends in prevalence of tobacco use 2000-2025, smoking accounts for 9% of all deaths worldwide, and more than half of smokers die from smoking-related diseases 1. China is the largest producer and consumer of tobacco in the world. In 2018, about 26.6% of adults (aged ≥15 years; 308 million in total) were current smokers and 44.9% of adults (515 million) were exposed to secondhand smoke at home 1. Exposure to cigarette smoke and secondhand smoke is very harmful to human health. There are over 7000 chemical components in tobacco smoke, of these, over 250 are toxic or carcinogenic, such as aldehydes, nitrides, and others that irritate the respiratory tract. Nicotine leads to tobacco addiction; benzpyrene, arsenic, cadmium and other components have carcinogenic effects and nitric oxide can reduce oxygen transport by erythrocytes. Smoking can damage nearly all organs of the human body and is one of the main risk factors for respiratory infection and infectious diseases in other systems, in a dose-dependent manner 2,3. In this review, we discuss the mechanisms and influence of smoking on infections in various systems, including the respiratory system, digestive system, and genital system, among others, in order to provide evidence for the active promotion of smoking cessation. DEVELOPMENTS Mechanisms of susceptibility The potential mechanisms of how cigarette smoke increases the risk of systemic infections are not completely understood. These may include alteration ABSTRACT Smoking is relevant to infectious diseases resulting in increased prevalence and mortality. In this article, we aim to provide an overview of the effects of smoking in various infections and to explain the potential mechanisms. We searched PubMed and other relevant databases for scientific studies that explored the relationship between smoking and infection. The mechanisms of susceptibility to infection in smokers may include alteration of the structural, functional and immunologic host defences. Smoking is one of the main risk factors for infections in the respiratory tract, digestive tract, reproductive tract, and other systems in humans, increasing the prevalence of HIV, tuberculosis, SARS-CoV, and the current SARS-CoV-2. Smoking cessation can reduce the risk of infection. Smoking increases the incidence of infections and aggravates the progress and prognosis of infectious diseases in a dose-dependent manner. Smoking cessation promotion and education are the most practical and economical preventive measures to reduce aggravation of disease infection owing to tobacco use.