Diarrhea and smelly stools are associated with diseases such as indigestion, intestinal flora imbalance, and intestinal tumors. In some patients, diarrhea is caused by indigestion, and the excreted stool contains a large amount of undigested food, which tastes foul because the nutrients in the food are not absorbed. When there is an imbalance of intestinal flora, intestinal function is affected, and diarrhea and foul-smelling stools are accompanied by reduced intestinal immunity, inflammation, and other factors. When the intestinal flora is imbalanced, the harmful bacteria in the intestine will overgrow, and the bacteria will react with food residues to produce foul-smelling metabolites, which will lead to especially foul-smelling stools. When intestinal tumor enters advanced stage, it will not only cause diarrhea due to disorder of intestinal function, but also cause tissue erosion and protein decay, so that the fecal matter with decaying substances will be excreted and smell relatively bad.