A breast abscess is an infection which infects the tissues of the breast. Breast abscess is caused by a common type of bacteria, Staphylococcus which is found on the normal skin. These bacteria enter the body through a crack or break in the skin, mostly through the nipple.The fatty tissues of the breast are infected thus resulting into swelling of the breast. The swelling suppresses the milk ducts. As a result, painful lumps are formed in the infected breast. This type of infection is usually caused by women who are breastfeeding. Infections which do no result from breastfeeding might be some type of breast cancer.