Enlargement of superficial lymph nodes at the back of the neck may be due to infection, autoimmune and allergic diseases, lymphoma, histiocytosis, metastasis of malignant tumors and so on. 1. Infection: it is a common cause of enlarged lymph nodes, and the pathogens include viruses, bacteria, parasites, fungi, mycoplasma and so on. 2. Autoimmune system diseases and allergic diseases: such as systemic lupus erythematosus, rheumatoid arthritis, drug allergic reaction and so on. 3. Lymphoma: this is a malignant tumor of lymph node origin, including Hodgkin’s lymphoma and non-Hodgkin’s lymphoma. 4. Histiocytosis, such as giant lymph node hyperplasia, lymphomatoid granulomatosis, etc. 5. Metastasis of malignant tumors: for example, leukemia, lung cancer, thyroid cancer, and so on. The causes of enlarged lymph nodes are more varied and complex, so you need to go to the hospital first and let the doctor diagnose before treatment to avoid delaying your condition.