Mastitis is an inflammation of the breast tissue, often caused by an infection. It commonly affects women who are breastfeeding, but it can also occur in women who are not nursing and in men. Symptoms may include swelling, redness, pain, and sometimes fever. The condition can develop when bacteria enter the breast tissue through a cracked nipple or blocked milk duct. Treatment typically involves antibiotics to clear the infection and pain relief measures. In some cases, drainage of any abscess may be necessary to promote healing and alleviate discomfort.