Normally, mixed breastfeeding and formula feeding does not cause diarrhea. However, there are some situations that can lead to diarrhea, such as improper feeding. The main components of breast milk and formula milk are roughly the same, so mixing formula milk and breast milk will not affect each other and cause diarrhea in babies. However, if too much formula is added, it will increase the burden on the baby’s stomach and intestines, causing gastrointestinal dysfunction, which will lead to diarrhea. Or if the baby is intolerant or allergic to certain ingredients in the formula, it will also lead to diarrhea. It is recommended to exclusively breastfeed, if the breast milk is not enough to meet the baby’s needs, you can add milk powder, the specific amount of milk powder should be added according to the baby’s condition.