A hard lump behind the ear may be caused by lymph node inflammation, sebaceous cysts and other diseases. 1. Lymph node inflammation: when the patient has inflammation of the external auditory canal, acute tonsillitis, oral inflammation, etc., the lymphatic vessels behind the ear may be involved, and lymph node inflammation occurs, resulting in hard lumps behind the ear. 2. Sebaceous cysts: mainly due to the sebaceous gland secretion behind the ear is blocked, resulting in long-term accumulation and retention of secretion, appearing behind the ear long hard lumps. Patients with a hard lump behind the ear should go to the hospital in a timely manner to clarify the cause of the disease and then give appropriate treatment and therapy under the guidance of the doctor.