The causes of four-month-old babies farting so smelly are usually indigestion, breast milk problems, gastrointestinal infections and so on. 1. Indigestion: If the baby also has white flaps or thin stools when farting is smelly, it is usually considered that the baby’s indigestion causes the baby’s fart to be too smelly. 2. Breastfeeding problems: When the mother’s diet is high in fat or protein, it may lead to smelly farts in the baby. Mothers can choose to adjust their diet to alleviate this situation. 3. Gastrointestinal infections: When a baby has an acute gastrointestinal infection, it will usually lead to a change in the stool pattern, an increase in the frequency of stools, and smelly farts. Four months baby fart stinks may also have other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.