Lymph nodes are an important part of the body’s immune system and can be found in multiple locations up and down the body, inside and out. Under normal circumstances, lymph nodes are no larger than 0.5cm in size and are not painful. When infection, inflammation or other causes of disease occur in the body, the lymph nodes can increase significantly in size and there can be obvious pain, which means that the corresponding parts of the body have undergone lesions. For example, breast cancer can lead to enlarged lymph nodes in the armpits, stomach cancer can lead to enlarged lymph nodes on the left supraclavicular region, and EBV infection or cytomegalovirus infection can lead to enlarged lymph nodes all over the body. In conclusion, lymph nodes are part of the immune system, and their abnormalities mean that the corresponding parts of the body are abnormal and should be examined and treated in time.