A red circle behind the head of a newborn baby may be related to prolonged pressure, or it may be caused by heat rash or infantile capillary hemangioma. 1. Prolonged pressure: If a newborn remains in a position of lying down for a long period of time, the skin behind the head and the pillow may rub and stimulate for a long period of time, which may cause a red circle behind the head. By changing the position in time, the symptoms will disappear soon. 2. Heat rash: common in the hot summer, due to the newborns stay in the higher temperature environment for a long time, resulting in more head sweating, long time by the sweat impregnation, may cause heat rash, which may cause the red circle behind the head, can also be accompanied by obvious itching, pain and other symptoms. 3. Infantile capillary hemangioma: it belongs to congenital benign hemangioma, which occurs in the head, face, neck and other parts of the body, and it can be manifested as a raised bright red lump on the local skin surface, which is not easy to fade away when pressed, thus it may lead to a red circle at the back of the head. The red circle on the back of the head of newborns may also be caused by other reasons. If accompanied by other obvious discomfort, it is recommended to consult a doctor as soon as possible to confirm the diagnosis of the causative factors and then give targeted treatment.