Sudden swelling of the cheeks under the ears can be caused by the following common reasons: a. Acute mumps, mumps is a viral infection that can manifest as significant swelling and pain in the parotid region, which can be detected by ultrasound examination with unclear borders, uneven echogenicity and inflammatory tissue changes in the parotid region, and the patient can be treated with symptomatic support by antiviral drugs such as ribavirin in drops and local topical application of Patients with mild symptoms can gradually relieve the swelling of cheeks in about a week. Second, purulent otitis media, purulent otitis media can also cause significant local swelling below the ear. Patients can go to the otology department of the hospital as soon as possible and give anti-infection treatment with cephalosporin antibiotics, which usually takes about two weeks, and the swelling and pain in front of the ear can be gradually relieved.