Breast infections are usually caused by bacteria. Rarely, breast infections lead to a breast abscess (a collection of pus in the breast). Mastitis refers to painful inflammation of the breast, which is usually accompanied by a breast infection.
(See also Overview of Breast Disorders Overview of Breast Disorders Breast disorders may be noncancerous (benign) or cancerous (malignant). Most are noncancerous and not life threatening. Often, they do not require treatment. In contrast, breast cancer can mean... read more .)
Breast infection
Breast infections Breast Infection A breast infection (mastitis) can occur after delivery (postpartum infection), usually during the first 6 weeks and almost always in women who are breastfeeding. If the baby is not positioned... read more do not often develop, except around the time of childbirth or after an injury or surgery. Having diabetes or taking corticosteroids by mouth increases the risk of breast infections.
The most common symptom of mastitis (including breast infections) is a swollen, red area that feels warm and tender. An uncommon type of breast cancer called inflammatory breast cancer Other characteristics 
can cause similar symptoms.
A breast infection is treated with antibiotics.
If taking antibiotics does not relieve the infection, doctors do an evaluation to check for cancer.
Breast abscess
Breast abscesses are less common than breast infections. An abscess may develop if a breast infection is not treated.
Doctors usually drain (aspirate) an abscess with a needle. Ultrasonography is used to guide placement of the needle. Sometimes doctors need to make an incision to drain the abscess.
Usually, women are also treated with antibiotics.
