Exhaled gas with a fishy odor is mainly the respiratory system may be out of the problem, the first consideration of lung abscess, followed by the possibility of respiratory tract infection. 1. Lung abscess: mostly inhalation, the liquid pollutants containing bacteria in the mouth are inhaled into the lungs by the organism, especially anaerobic bacteria. Bacteria that enter the lungs stimulate the lungs to produce inflammation, tissue necrosis, and finally the formation of pus accumulates in the pus cavity, and over time there will be fishy gas exhaled. 2. Respiratory tract infections: seen in the respiratory system acute infections, such as acute tonsillitis, acute bronchitis, may also be an acute attack of chronic disease, bacterial metabolites accumulate, the smell of corruption is similar to the smell of fish. If there is a fishy odor exhalation should not be ignored, should promptly seek medical attention.