Farting is a normal phenomenon. The medical term for farting is anal exhaust, and the odor of the expelled gas is related to the composition of the gas. Anal exhaust is a normal physiological phenomenon, part of the intestinal gas comes from swallowing saliva, food and swallowed air, the main component for the colorless and tasteless nitrogen. The other part is mainly from the residue of food that has not been fully digested and absorbed, which is fermented by the intestinal bacteria in the intestinal tract to produce hydrogen, ammonia, methane, hydrogen sulfide and other gases, of which ammonia and hydrogen sulfide have an irritating odor, and these gases are discharged along with the gastrointestinal tract movement, and ultimately through the anus. The proportion of odorous gases determines the size of the odor of the gas expelled from the anus. When there are obvious abnormalities in the nature and pattern of anal discharge, it is recommended to go to the hospital for examination and treatment to avoid delays.