The fishy smell of exhaled gas is only a clinical manifestation, mainly due to the presence of possible diseases of the respiratory system. More common are infections of the respiratory tract such as acute tonsillitis, acute attacks of chronic tonsillitis, acute pharyngitis, nasopharyngitis, acute attacks of chronic pharyngitis, nasopharyngitis, and also severe bronchitis. This is usually caused by purulent bacterial infections and may be combined with a small amount of anaerobic bacterial infections, when the exhaled breath has a putrid, fish-like odor from bacterial inflammatory metabolites. Also seen in chronic pulmonary heart disease is more serious, there may be a combination of pulmonary encephalopathy, this time there will be respiratory failure resulting in respiratory acidosis, the exhaled breath has a fishy smell.