Bumps behind the ears can be caused by the following diseases: 1. swollen lymph nodes behind the ears, which can be secondary to local inflammation or malignant tumors with localized metastases in the nodes, and the patient may also show pain, fever, or significant anemia, loss of appetite, and weight loss. 2. sebaceous cysts or subcutaneous fibromas that occur under the skin or in the skin, because the head and face are rich in sweat glands. The head and face are rich in sweat glands, so it is easy to block the sweat ducts and secondary sebaceous cysts, which can appear as local bumps or lumps in the early stage. If infection occurs, it may also show symptoms of redness, swelling and pain, and if necessary, surgical excision or incision and drainage may be required.