Swollen lymph nodes under the left ear can be classified into two causes: first, inflammation of the lymph nodes in an independent individual; second, inflammatory reaction of the surrounding tissues and stimulation resulting in swollen lymph nodes. For example, a single lymphadenitis or lymphoma can cause swollen lymph nodes, while peripheral otitis externa, otitis media, tonsillitis, maxillofacial interstitial infection, acute epiglottitis, etc., including mumps can indirectly cause swollen lymph nodes under the left ear. The treatment plan is still mainly based on anti-inflammatory and anti-infection. If the surface of the lymph node suddenly increases or ruptures, ultrasound or biopsy is needed to clarify the diagnosis.