The causes of acute bronchitis include microorganisms, allergic reactions, and physical and chemical injuries. 1. Microorganisms: common ones include viruses, bacteria, chlamydia, mycoplasma and so on which can invade the human body and stimulate the bronchial mucosa to have inflammatory reaction. Viruses include coronavirus, influenza virus, adenovirus, etc. Bacteria include Streptococcus pneumoniae, Haemophilus influenzae, etc. Mycoplasma and Chlamydia infections are also common. 2. Allergic reaction: pollen, dust, animal fur and excreta are often inhaled through the respiratory tract to trigger an allergic reaction, resulting in acute inflammatory reaction of the trachea and bronchial tubes. 3. Physical and chemical damage: cold air, dust, irritating gases, such as sulfur dioxide, ammonia, chlorine, will stimulate the trachea, resulting in acute damage and inflammation of the mucosa of the trachea. Acute bronchitis causes more, once the cough, fever, tightness, chest tightness and other symptoms need to consult a doctor in a timely manner, clear causes for targeted treatment.