Why does a blocked milk duct cause a breast lump?

Milk normally moves from breast tissue through ducts toward the nipple. When flow slows at one point, milk can collect behind it and the surrounding tissue may become swollen and inflamed. This produces a localised, firm or wedge-shaped area that may feel tender. It can change after feeding or expressing, although the breast may remain sensitive for a while.

Breast lumps have many possible causes. A lump that does not improve, changes in the skin or nipple, or a lump outside the breastfeeding context deserves clinical assessment rather than a self-diagnosis.

Continue feeding or expressing according to your baby’s needs, using a comfortable position and avoiding forceful massage. Gentle touch, rest, fluids, and a cool pack after feeding may ease swelling. Avoid tight clothing and repeated extra pumping, which can increase breast stimulation. A lactation professional or clinician can help if attachment or milk removal is difficult.

Contact a clinician promptly if the lump is accompanied by fever, chills, worsening redness, increasing warmth, pus, or feeling unwell. Arrange an assessment if it persists despite simple measures, returns frequently, or is associated with nipple discharge, skin dimpling, or a change in nipple position.

Ask whether the lump fits a blocked duct, how to adjust feeding or expressing, and whether an examination or imaging is needed. Ask which signs suggest mastitis or an abscess and when to return if the area does not settle.