Unopened expired yogurt is not recommended for consumption. The process of making yogurt is pasteurized, but it does not kill all the bacteria, but retains some lactic acid bacteria, etc. Expired yogurt may have bacteria multiplying, including pathogenic bacteria as well as molds, which may cause gastrointestinal diseases if consumed. Usually active Lactobacillus is the main strain of bacteria in yogurt, which helps regulate intestinal flora and improve symptoms such as indigestion and bloating. The nutrients in expired yogurt will be destroyed, and the activity and number of beneficial bacteria such as Bifidobacterium, Lactobacillus acidophilus and Lactobacillus bulgaricus will be drastically reduced, thus gradually losing its role in regulating the intestinal tract. Expired yogurt can also breed a large number of harmful bacteria, such as Staphylococcus aureus, Mycobacterium tuberculosis, rotavirus, etc., and may even contaminate the toxin. Human consumption will not only cause symptoms such as abdominal pain and diarrhea, but may also lead to food poisoning reactions. The active lactic acid bacteria in yogurt can make the shelf life of yogurt shorter because the active lactic acid bacteria in yogurt only remain stationary at a temperature of 0℃-4℃. As the temperature rises the lactic acid bacteria will multiply rapidly and produce acidic metabolites, at which point the nutritional value of the yogurt decreases and it becomes an acidic dairy product without active bacteria, and the taste will change accordingly. The shelf life of bagged yogurt is usually about one week, and must be refrigerated at 2°C-6°C. Boxed yogurt has a shelf life of 18-21 days. It is recommended to check the shelf life before consumption to avoid discomfort caused by the accidental consumption of expired yogurt.