Sulfur trioxide is toxic and harmful. Sulfur trioxide is a colorless, easily sublimated solid at room temperature, which is soluble in water and reacts with water to form sulfuric acid and gives off a lot of heat. Therefore, it is also called sulfuric anhydride. Sulfur trioxide has the same toxicity as sulfuric acid, and has a strong irritating and corrosive effect on skin, mucous membranes and other tissues. When it touches the skin, it produces a lot of heat and acid, which will burn the skin; when it enters the eyes, it produces a lot of heat and acid, which will damage the eyes and cause the cornea to become cloudy, resulting in blindness; when it is inhaled, it produces heat and acid, which will damage the mucous membranes of the respiratory tract, resulting in respiratory difficulties; when it is taken orally, it will cause burns on the digestive tract, resulting in the formation of ulcers. Severe cases may have gastric perforation, shock and so on. Care should be taken to protect against contact with and inhalation of sulfur trioxide in daily life.