Pain behind the ear may be due to acute mastoiditis, subperiosteal abscess behind the ear and infection of the 1st gill slit cyst and fistula. 1. Acute mastoiditis: the common cause is acute bacterial infection caused by acute suppurative otitis media spreading to the mastoid. The patient’s mastoid skin is swollen, and the groove behind the ear is red, swollen and painful. 2. Posterior subperiosteal abscess and fistula: Due to acute attack of chronic suppurative otitis media, cholesteatoma or acute mastoiditis, pus accumulates in the mastoid cavity and gathers in the lower part of the posterior mastoid ossicles, forming a posterior subperiosteal abscess, and a posterior fistula can be formed after the fracture. The pain behind the ear is accompanied by headache on the same side. 3. The first gill slit cyst and fistula infection: this disease is caused by the embryonic development of the first and second gill arches are not normal fusion. Internal fistula is located in the cartilaginous part of the external auditory canal, the ear screen, mastoid, etc., so it is also known as the ear neck fistula or cyst. When a cyst or fistula develops an infection behind the ear, it can manifest as pain behind the ear. Pain behind the ear may also be other reasons, it is recommended that patients go to the hospital, identify the cause of treatment, do not use drugs without authorization, so as not to cause adverse consequences.