The main causes of swelling and pain below the base of the ear include inflammation of lymph nodes, sebaceous cysts, first parotid fissure cysts, and acute parotitis. 1. Inflammation of lymph nodes: As there are more lymph node tissues under the root of the ear. When lymph node inflammation occurs, it can cause local redness, swelling and pain. Acute otitis externa and acute tonsillitis can trigger lymph node inflammation here. 2. Sebaceous cysts: If sebaceous cysts appear below the root of the ear, they can cause localized swelling, and secondary infection will lead to localized pain. 3. First gill slit cyst: This is a congenital disease caused by abnormal development of the first gill slit. It may appear as a limited elevation behind the ear or below the base of the ear. If infection occurs here, it can cause localized redness, swelling, heat and pain. 4. Acute parotitis: An acute inflammatory lesion of the parotid gland caused by a pathogenic microbial infection. It can be characterized by pain, redness and swelling in the face and below the ears, usually affecting mouth opening and eating. As you can see, if you have pain and swelling below the ear, it is recommended that you go to a regular hospital in a timely manner, to identify the cause of the disease and target treatment.