Lymph is a clear fluid that travels through the breast carrying away waste from the breast to the lymph nodes where bacteria and other foreign particles are filtered out. From there lymph is transported into the axillary lymph vessels and the nodes under the armpits.

Most lymph drainage of the breast is via the axillary lymph nodes, proceeding from there to the supraclavicular lymph nodes. Drainage from the medial part of the breast is via the internal mammary nodes which lie beneath the ribs and lateral to the sternum.