The increase in dental caries in children is not unrelated to the regular consumption of lactic acid bacteria beverages. Because certain strains of lactic acid bacteria play an important role in the formation of dental caries, they must be rinsed with boiled water immediately after drinking lactic acid bacteria beverages such as yogurt. In addition, children avoid drinking sour milk on an empty stomach. The acidity of lactic acid bacteria for growth is above pH 4-5, while the pH of human gastric juice is between 1-3 and the pH of intestinal fluid is between 5-7. Therefore, lactic acid bacteria are in the intestine. The tract grows and reproduces, but it is easily killed by gastric acid in gastric juice. When fasting, the acidity of human gastric juice is below pH 2 and the gastric juice is diluted after meals. The pH can rise to 3~5. It can be seen that drinking sour milk on an empty stomach causes lactic acid bacteria to be easily killed and the health care function is weakened; while drinking sour milk within 2 hours after a meal, lactic acid bacteria should not be killed.