Lymph nodes at the back of the head of a five-month-old baby are usually a normal physiological phenomenon, but if there are swollen lymph nodes and pain when pressed, you should seek medical attention. Lymph nodes, as part of the lymphatic system that makes up the human body, include reticuloendothelial cells and lymphatic tissues, while lymphs throughout the body are interconnected with each other through lymphatic vessels. Among them, the lymphocytes generated by the lymph nodes have certain immune functions, which can remove, filter and phagocytose the bacteria in the lymphatic vessels and so on, and have a certain protective effect on the baby’s health. And five months of the baby’s lymphatic system development is relatively vigorous, so when touching the back of the baby’s head appeared around the size of a soybean, free movement, squeeze the painless lymph nodes, generally do not have to deal with are normal physiological phenomena. If you find that the baby lymph nodes are string-like, hard, obviously enlarged, press the baby to feel obvious pain, or a short period of time to increase the size or increase should seek medical attention.