Level 1: Causes of infant diarrhea and vomiting 1.1 Unclean food There are bacteria, viruses, parasites and other pathogenic microorganisms in food. If it is not processed thoroughly or washed, it will be ingested into the human body, causing symptoms such as diarrhea and vomiting. 1.2 Immature Digestion: The digestion of infants is not mature enough. It is difficult to digest some foods and may easily cause diarrhea, vomiting and other problems.