Lymph node structure is a small ball-shaped part of the immune system. Lymph nodes are spread throughout the body, joined together by duct (lymphatic vessels), and serve to detect and trap foreign particles. Lymph nodes in the groin are very numerous, and in the chest, neck, pelvis and armpits. These are inflamed or elongated by various diseases as a throat infection or cancer. When swollen lymph nodes appear suddenly and is painful, it is usually due to an injury or infection, while slow and painless swelling may be due to cancer or tumor. However, when a node is hard and the area is red and warm it is a concern, so it is advisable to visit the doctor. The location of the node is another factor to consider at the time of diagnosis. For example, an inflamed lymph node in the axilla often a symptom of a benign local inflammation.