A bulge on the back of the neck may be caused by lipoma, epidermal cyst, liposarcoma and other diseases. 1. Lipoma: Lipoma may be related to heredity, there may be lipoma tumorigenic factor in the patient’s body, once it is activated, it may lead to abnormal proliferation of normal fat cells, thus forming lipoma, which will be manifested as a bulge on the back of the neck, and may be accompanied by pain and numbness. 2. Epidermoid cysts: Epidermoid cysts may be caused by skin injury resulting in epidermal cell proliferation, and patients may have round or ovoid nodules, which may be accompanied by redness, tenderness and other symptoms. 3. Liposarcoma: Liposarcoma may be related to trauma, hematoma, viral infection or radiation therapy, etc., and the patient may have soft tissue lumps, making the bulge on the back of the neck, which is usually not accompanied by other uncomfortable symptoms in the early stage. Patients with a bulge on the back of the neck are recommended to be admitted to the hospital for examination and standardized treatment after identifying the cause.