Diarrhea in four-month-old babies is usually caused by diet or cold in the abdomen. For breastfed babies, if the mother does not eat properly or does not pay attention to dietary hygiene, it is possible that the milk secreted to feed the baby will cause the baby to have diarrhea. If the mother herself has diarrhea symptoms and continues to breastfeed, it is possible that the baby will also have diarrhea. For milk-fed babies, it is important to pay attention to the safety of the milk and milk allergies, as well as the hygiene of the bottle, and if the baby has added complementary foods, it is also important to pay attention to the hygiene of the complementary foods and whether they can be digested by the baby. In addition, if the baby does not pay attention to abdominal warmth, it may be caused by abdominal cold diarrhea, it is recommended that if the baby has a mild diarrhea can be temporarily observed, or if necessary, treated with oral mamma-aid. However, for safety reasons it is best to take your baby to the hospital and use medication only when necessary under the guidance of your pediatrician.