Why does my baby have diarrhea after drinking formula milk?

There may be several reasons why a baby develops diarrhea after drinking formula, with the most common being lactose intolerance and allergic reactions. Lactose intolerance occurs when a baby lacks sufficient lactase, the enzyme needed to fully digest lactose in formula, leading to symptoms such as diarrhea. In such cases, parents can try switching to low-lactose or lactose-free formula to help alleviate the baby's symptoms. Allergic reactions are another common cause of diarrhea in babies after consuming formula. Some babies may be allergic to certain ingredients in the formula, such as cow's milk protein, which can trigger symptoms including diarrhea.