Babies crying on breastfeeding may be caused by breastfeeding problems, oral diseases, gastrointestinal diseases, vitamin D deficiency and other conditions. 1. Breastfeeding problems: If breastmilk is insufficient, resulting in sucking difficulties for the baby, and the feeding method is inappropriate, e.g. the breast blocks the baby’s nostrils, resulting in the baby not being able to breathe normally, etc., all of these can lead to babies crying at breastfeeding. 2. oral disease: if the baby’s mouth ulcers, herpes, milk will stimulate the oral cavity to produce pain, causing crying. 3. gastrointestinal diseases: gastrointestinal diseases such as indigestion, colic, etc. may also cause babies to cry at breastfeeding. 4. Vitamin D deficiency: Vitamin D deficiency at the beginning is mainly manifested as increased nerve excitability and other non-specific manifestations, such as irritability, irritability, etc., may also lead to babies crying at breastfeeding. There may be other reasons why babies cry when they are breastfed, so it is recommended to go to the hospital in time, complete the examination to clarify the cause of the disease, and then give targeted treatment under the guidance of the doctor or treatment.