A large and hard bump on the back of the ear is commonly caused by: 1. Sebaceous cysts, which can occur after prolonged friction or improper cleaning behind the ear. This is caused by a blocked hair follicle and requires a visit to the hospital for clarification. If the disease is present, it can usually be removed under local anesthesia. If left untreated, redness, swelling and pain may occur at a later stage, and even break down and flow pus. 2. Swelling of lymph nodes is often caused by infection of surrounding tissues, such as inflammation of wisdom teeth and parotid infection. It can be clarified through blood tests and ultrasound, and can usually be relieved by antibiotic treatment. 3. Some other diseases may also cause swollen lymph nodes, such as autoimmune system diseases, lymphoma, and even lymph node metastasis of malignant tumors. It is necessary to further investigate CT and lymph node biopsy to clarify. Normally, you cannot eat too spicy food during the enlargement, and if the swelling is large, you need to go to the hospital promptly and clarify the cause.