The harm of sulfur dioxide in the respiratory tract is mainly because it is easily soluble in water, most of which is dissolved in the body fluid of the upper respiratory tract, and forms corrosive sulfite, sulfuric acid and sulfate on the moist mucosa, which enhances the stimulation effect. The smooth muscle of the upper respiratory tract has peripheral nerve receptors. When stimulated, it will produce a constriction reaction, which makes the lumen of trachea and bronchus shrink, and the airway resistance increases. The blocking effect of upper respiratory tract on sulfur dioxide can reduce the sulfur dioxide entering the lung and stimulate it to a certain extent. However, sulfur dioxide entering the blood can still reach the lung through blood circulation to produce stimulation.

Sulfur dioxide can be absorbed into the blood, causing toxic and side effects on the whole body. It can destroy the activity of enzymes, thus significantly affecting the metabolism of carbohydrates and proteins, and causing certain damage to the liver. Animal experiments showed that the immune function of the body was obviously inhibited after sulfur dioxide poisoning.

When the concentration of sulfur dioxide was 10-15ppm, the ciliary movement and the secretion function of mucous membrane were inhibited. When the concentration reaches 20ppm, it causes cough and irritates eyes. If the inhalation concentration is 100ppm 8 hours a day, obvious irritation symptoms appear in the bronchus and lungs, and the lung tissue is damaged. When the concentration reaches 400 ppm, it can cause dyspnea. Sulfur dioxide is inhaled together with dust. Aerosol particles can carry sulfur dioxide to the lungs and increase the toxicity by 3-4 times. If metal particles are adsorbed on the surface of the dust, the sulfur dioxide will be oxidized to sulfuric acid fog under its catalysis, and its stimulating effect is about twice as strong as that of sulfur dioxide. Living in the air pollution environment for a long time, the combined action of sulfur dioxide and dust can promote the proliferation of alveolar fibers. If the proliferation of the scope of extensive spread, the formation of fibrous lesions, the development of fiber rupture can cause emphysema. Sulfur dioxide can enhance the carcinogenic effect of benzo (a) pyrene. Incidence rate of animal incidence rate of lung cancer is higher than that of single factor under the combined action of sulfur dioxide and benzo (a) pyrene. Animal can be induced flat cell carcinoma in the short term.