A reactive lymph node is an enlarged lymph node, which is commonly the result of an infection. The enlargement of the node is a feedback mechanism of the immune system when foreign objects, such as viruses, bacteria or cancer cells, invade the body.
The lymph nodes are distributed throughout the body and form an integral part of the lymphatic system. Lymphocytes and macrophages, which combat disease-causing elements, are clustered around these nodes. During exposure to harmful substances, these nodes swell in response to elevated levels of inflammatory cells in the affected area. Typically, enlargement of the lymph nodes occurs in the neck, armpits, groin and under the chin.