The main causes of smelly farts include excessive protein intake, indigestion, and stomach disorders. 1. Excessive protein intake: High protein foods include meat, milk and eggs. A large amount of high protein food enters the intestinal tract, decomposes and ferments under the action of intestinal flora, and produces amines and other smelly substances, which are discharged from the body with the gas and produce smelly farts. 2. Indigestion: food accumulates in the intestines because it is difficult to be digested, and through fermentation, decomposition and other chemical effects, foul-smelling substances such as volatile amino acids, short-bonded fatty acids and other foul-smelling gases are produced, which are discharged with the intestinal peristalsis and produce smelly farts. 3. Gastric diseases: chronic gastritis, gastric ulcer and other patients, due to gastric mucosa damage, gastrointestinal dysfunction, food digestion difficulties, which leads to food accumulation, fermentation in the intestine, resulting in foul-smelling gas. Old smelly farts may also have other reasons, if other symptoms, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.