Most people do not usually develop diarrhea after the MMR vaccine, which needs to be considered as a result of poor diet or illnesses such as irritable bowel syndrome or enteritis. The full name of the MMR vaccine is MMR3, which can prevent three common childhood infectious diseases: measles, mumps, and rubella. Adverse reactions to MMR vaccine may include swelling of the cheek or cervical lymph nodes, or mild fever and rash, and generally do not cause diarrhea. For people with diarrhea symptoms, the first consideration is improper diet, excessive intake of spicy and stimulating foods or overeating. Secondly, it may also be caused by diseases, such as irritable bowel syndrome, enteritis, etc., can cause diarrhea. After the MMR vaccination, pay more attention to protect the injection site to avoid infection. If the symptoms of diarrhea are more serious, it is recommended to seek medical examination to clarify the diagnosis.