Sour stool may be normal, or it may be caused by poor diet or indigestion. 1. Normal phenomenon: It is normal for infants to have sour stools without foam if they are usually breastfed. If the baby is not breastfed but is fed with complementary foods and the stools have been normal, and then suddenly appears to have a sour taste, it may be due to indigestion. 2. Unreasonable dietary structure: If the dietary structure is not reasonable, it may also lead to the sour smell of stools. Due to the frequent consumption of spicy and stimulating foods, fried foods, which contain chemical substances, when decomposed in the intestinal tract, they often produce a lot of metabolic wastes with a sour odor, leading to the occurrence of a sour smell of stools. 3. Indigestion: If you eat too much protein food, you will have indigestion. Protein can reduce the concentration of gastric acid and neutralize gastric acid, which makes the protein absorption and digestion poor, and the bacteria in the intestinal lumen can decompose and metabolize it, which may lead to acidic stools. If there is a sour odor in the stool, it is recommended to closely observe the situation, and seek medical advice for symptomatic intervention in case of abnormality.