Three blue patches on baby’s back may be Mongolian spots, hemangiomas, subcutaneous petechiae, etc. 1. Mongolian spots: the appearance of green patches on the back is considered to be skin Mongolian spots, which are caused by congenital factors and are related to the active melanocytes in the dermis. 2. Hemangioma: It is necessary to observe whether there is any change or not, and if there is any abnormality, it is necessary to diagnose and treat in time. 3. Subcutaneous petechiae: due to trauma or abnormalities in blood clotting function and platelets, babies may develop green petechiae under the skin, which will not fade away after being pressed. As this symptom alone can not determine the disease, and do not rule out other factors. It is recommended that the patient consult a doctor in time to clarify the cause of the disease and give targeted treatment.