There is a small bulge behind the baby’s ear root which may be caused by enlarged lymph nodes behind the ear, sebaceous cyst, mastoid osteoma, etc., and it is mostly treated with drugs or surgery. 1. Enlarged lymph nodes behind the ear: located in the mastoid surface behind the ear, between the sternocleidomastoid muscle stop, infection is the most common factor, can be anti-infective treatment under the guidance of the doctor, such as cefaclor, cefixime, etc., if the symptoms are more serious should also be sent to the hospital for incision and drainage surgery. 2. Sebaceous cysts: can also appear behind the ear root with a small bulge, but no other adverse reactions, generally do not need to do special treatment, if the symptoms are more serious, then the doctor combined with the baby’s general condition, local anesthesia surgery to remove. 3. Mastoid osteoma: it is a benign tumor, if the lump is small and asymptomatic, no special treatment is needed. If the lump increases in size and causes obvious symptoms, it should be completely removed by surgery. All of the above medicines should be used under the guidance of doctors, avoiding self-medication. There are many other possibilities for a small bulge behind your baby’s ear, so it is recommended to consult a specialist for evaluation and treatment.