Sulfur dioxide (SO2) is a colorles, highly toxic gas with a choking or suffocating odor. It is used as a pharmaceutical aid and antioxidant. It reacts easily with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles. About 99% of the sulfur dioxide in air comes from human sources. The main source of sulfur dioxide in the air is industrial activity that processes materials that contain sulfur, eg the generation of electricity from coal, oil or gas that contains sulfur. Some mineral ores also contain sulfur, and sulfur dioxide is released when they are processed. In addition, industrial activities that burn fossil fuels containing sulfur can be important sources of sulfur dioxide. Sulfur dioxide affects human health when it is breathed in. It irritates the nose, throat, and airways to cause coughing, wheezing, shortness of breath, or a tight feeling around the chest. The effects of sulfur dioxide are felt very quickly and most people would feel the worst symptoms in 10 or 15 minutes after breathing it in. Sulfur dioxide is used to increase the storage life and preserve the color and flavor of fruits and vegetables and as a disinfectant in breweries, wineries and food factories. It prevents the formation of nitroamines in beer and reduces free chlorine after water treatment. It is used as a bleaching agent in the textile, paper pulp, wool and fresh produce industries and as a fumigant for grain and against lice and mites in veterinary practice. It also serves as a chemical intermediate in the manufacture of chlorine dioxide, sodium sulfate, thionyl chloride and organic sulfonates. It is used as a reducing agent of iron in mineral processing, as a cleaning agent for metallic oxides, as an oxidizing agent in lithium batteries, as an oxygen scavenger and extractive solvent in petroleum refining, in glass manufacture and as a neutralizing agent. SO2 can be generated endogenously in mammals. In contrast to the toxic effects of SO2, protective effects have also been found in mammals. Endogenous SO2 has antioxidant, anti-inflammatory, anti-hypertension, and anti-atherogenic effects and regulates vascular tone and cardiac function in mammals. SO2 may have a dual role in regulating physiological and pathophysiological effects in mammals. Studies have shown that SO2 can also regulate levels of lipid metabolism. In male Sprague–Dawley rats on a normal or a high cholesterol diet, inhalation of 5 ppm and 10 ppm SO2 gas (for 14 days) increased plasma triglyceride levels and decreased high-density lipoprotein cholesterol levels. However, in rats treated with a high cholesterol diet for 8 weeks, plasma total cholesterol increased and high-density lipoproteincholesterol decreased. After treatment with an SO2 donor the plasma levels of triglyceride and low-density lipoprotein cholesterol were markedly decreased. In addition, the SO2 donor significantly decreased atherosclerotic lesions. These data suggest that SO2 regulates lipid metabolism. The mechanism may be related to upregulation of the disturbed endogenous H2S pathway, increased plasma glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) activities, aortic tissue SOD1 and SOD2 protein expression, and decreased malondialdehyde generation. The antioxidant effect of SO2 might involve one of these mechanisms, which could directly prevent the progression of atherosclerotic lesions. Sulfur dioxide and its derivatives have significant vasodilatory effects. SO2 decreased systolic blood pressure in spontaneously hypertensive rats which may be related to its vasorelaxing effect. Compared with exogenous SO2 vasoactive effects, it was discovered that endogenous SO2 had an important vasorelaxing function which is necessary for maintaining normal blood vascular tone.