The patient has a small bag behind the ear, accompanied by local pressure pain. In this case, there are two etiologies: one is caused by swollen lymph nodes behind the ear; the other is caused by an attack of the sebaceous gland behind the ear. Patients need to go to the hospital to check the local ultrasound to confirm the diagnosis, as follows: a. Swollen lymph nodes behind the ear: most of them are caused by acute inflammatory infections, often secondary to acute otitis media and acute tonsillitis. In terms of treatment, symptomatic anti-inflammatory treatment, antibiotics and local hot compresses are needed to gradually improve. Second, post-auricular sebaceous cysts: cysts are caused by chronic inflammatory stimulation of the local skin for a long time and blockage of the hair follicles caused by bacterial contact, and patients will experience local swelling and pain. In the treatment, local surgical excision is required to cure it completely.