The back of the baby’s head has a depression may be the fontanel, skull bone overlap and other physiological phenomena caused by, but also may be vitamin D deficiency, trauma caused by, you can take oral vitamin D and other medications, surgical treatment, and so on. 1. Unclosed fontanel: The fontanel is not closed when the baby is born, and usually closes within six weeks after birth, and the fontanel feels concave, which is a physiological phenomenon and does not need to be treated. 2. Skull bone gap overlap: because of the head extrusion caused by the overlap of the bone gap during delivery, do not need other special treatment, as the baby grows up will slowly improve. 3. Vitamin D deficiency: Especially for babies around three months old, the lack of vitamin D leads to the obstacle of calcification of the skull, resulting in the formation of ping-pong head, and there is a sense of depression when the skull is pressed. You can take vitamin D orally for a period of time as prescribed by your doctor, and if necessary, you can take calcium supplements. 4. Trauma: If there is no depression in the back of the head, and suddenly there is obvious redness, swelling, heat and pain in the tissues at the back of the head, it is necessary to seek surgical treatment, so that the surgeon can assess whether surgery and other treatments are needed. There may be other reasons for the depression at the back of the baby’s head. It is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy. All of the above medications should be used under a doctor’s supervision.