There are many reasons why babies’ chests bulge, mainly due to the following reasons: 1, newborn babies are affected by the mother’s estrogen, there will be a chest bulge, which will disappear on its own after a week or so, this phenomenon is very common in newborn babies, and parents don’t need to worry about it too much. 2, babies’ endocrine disorders, babies’ endocrine disorders can also cause chest bulge, and this is a common example, not serious, don’t need to worry about it, mothers need to take good care of the baby, scientific feeding, the bulge will slowly disappear after a period of time. This is not serious, don’t worry, the mother should take good care of the baby, scientific feeding, after a period of time, the bump will slowly disappear. 3, if the baby long time chest bump does not disappear, we should consider whether it is caused by disease, for example, may be improper care of babies, infections, mammary glands slightly hyperplasia, enlargement, etc., this time, the mother must not be negligent, we should take the baby to the hospital in time to do a checkup, to find out the cause of the disease, and actively treatment.