Common causes of lumps in the neck under the left ear include enlarged lymph nodes, sebaceous cysts, fibroids, and tumors. 1. Enlarged lymph nodes: usually due to bacterial infection causing inflammation of lymph nodes, which leads to reactive hyperplasia and enlargement of lymph nodes, and mostly accompanied by painful symptoms. Lymph node enlargement usually occurs in the neck, groin and other parts of the body, so it can cause the manifestation of a lump in the neck of the left ear. 2. Sebaceous cysts: usually caused by sebaceous gland ducts blockage, abnormal secretion and other reasons, resulting in sebum accumulation under the skin, and easy to make bacterial growth, which is manifested as lumps on the neck below the left ear. 3. Fibroma: it is related to heredity and overgrowth of skin fibroblasts, which makes skin fibers proliferate abnormally, resulting in lumps on the skin and itchy symptoms, which can also be manifested as lumps on the neck under the left ear. 4. Tumor: for example, lipoma, lymphoma, parotid tumor or when nasopharyngeal, thyroid and other parts of the tumor metastasis to the lower left ear, can lead to lumps on the neck below the ear. If there is a lump on the neck under the left ear, it is recommended to consult a doctor in time and have a systematic examination to make a clear diagnosis.