Nicotine is mainly found in cigarettes, people in the long-term smoking will not only produce excessive dependence, but also on health hazards. Nicotine can cause damage to the human nervous system, digestive system, respiratory system and circulatory system: 1, the nervous system: when smoking nicotine can stimulate the brain to release dopamine, producing the illusion of mental relaxation, long-term smoking will not only cause addiction, but also damage the nervous system, resulting in different degrees of language, memory, feeling and other abilities to decline. In addition, if adolescents smoke, nicotine will also have an impact on brain development, attention, learning, self-control and other hazards; 2, digestive system: because nicotine in the combustion, will produce alkaloids and other chemicals, there is a toxic effect on the human digestive system, in the long run can appear nausea, vomiting, stomach burning and other uncomfortable symptoms, research shows that the incidence of stomach cancer in regular smokers 3, respiratory system: long-term smokers often have yellowing teeth, gum bleeding and other oral problems. The nicotine in the smoke inhalation, but also quickly through the nasal cavity, throat, lungs, etc., may induce respiratory diseases, such as acute eosinophilic pneumonia, diffuse alveolar hemorrhage and other acute lung injury, as well as stimulation of the throat, causing coughing, dry throat and other adverse reactions; 4, circulatory system: nicotine in tobacco can affect the body’s myocardial tissue, stimulating vasoconstriction, causing smokers Heart rate is too fast, blood pressure increases and other problems, thus increasing the incidence of hypertension, stroke and other cardiovascular diseases.