Infections of the breast are common. They can be caused by bacteria, fungus, and mycobacteria (tuberculosis is an example of a mycobacteria).

Bacterial Breast Infections

Bacterial breast infections are usually caused by normal skin bacteria, such as Staphylococcus aureus and Streptococcus. They can occur when bacteria enter the breast tissue through cracks in or around the nipple, such as during breastfeeding. Bacterial infections can also occur in areas of bruising, trauma to the breast (including nipple piercing), or after a biopsy or surgery.

Bacterial breast infections typically involve the fatty tissue in the breast. Swelling, localized pain, redness, and fever are the most common symptoms of a bacterial infection. When a breast infection causes a collection of pus, it is called an abscess. Most bacterial breast infections respond to antibiotics but in more severe cases, when an abscess forms, aspiration (removing the infected fluid with a needle) is often required. For large collections of pus, surgical drainage may be necessary.

A specific type of bacterial breast infection is seen in cigarette smokers. These bacteria are called anaerobic bacteria—bacteria that can live without oxygen. This infection, called Zuska’s disease, is associated with recurrent draining abscesses in and about the nipple. Cigarette smoking causes clogged ducts, which trap the anaerobic bacteria. This in turn leads to the infection and collections of pus. Draining tracts, called fistula, are also seen. Antibiotics and surgery can help but not cure Zuska’s disease. Stopping smoking cigarettes is necessary to curing these infections.

Fungal Breast Infections

The most common fungal infections of the breast involve the skin on the undersurface of the breast and the fungus Candida albicans. Cutaneous candidiasis is a rash that frequently itches and may smell “yeasty.” It is common in women who are diabetic, have large breasts, are on immunosuppressive medications (such as steroids, transplant medications, cancer medications) or who have immunosuppressive or autoimmune disease (such as HIV or rheumatoid arthritis and scleroderma), and during warm weather. It is usually treated with an antifungal cream or lotion.

Fungal infections within the breast may be seen in patients whose immune systems are extremely low. These fungal infections are more than skin deep and require either oral medications or intravenous medications. In certain regions, specific fungal infections may be more common; for example, coccidiomycosis is seen in the Southwest and blastomycosis is seen in heavily forested regions, such as the upper Midwest. These infections are diagnosed by tissue cultures.

Tuberculosis of the Breast

Tuberculosis, or TB, of the breast is very uncommon in the United States. It is most often seen in people who come to the United States from areas where TB is common and more rarely in Americans who have HIV or severe immunosuppressive disease. TB of the breast may present as a breast mass with abnormal imaging or as a draining wound. Cultures specific for TB are required to confirm the diagnosis. TB medications will treat this disease.

Other Conditions That May Mimic Breast Infection

Idiopathic granulomatosis—This disease usually presents as a breast mass that may have imaging findings that resemble breast abscesses. Aspiration, tissue culture, and tissue biopsy are required in this condition.

Inflammatory breast cancer—Although many women worry about “inflammatory breast cancer,” this cancer is very rare. Most physicians will start treating a red, warm breast that is swollen and tender with antibiotics. If the patient does not improve, biopsy is considered. Other findings of inflammatory breast cancer, including enlarged lymph nodes under the arm, less tenderness than expected, and skin that appears like an orange peel (peau d’orange), may increase a doctor’s suspicion. In these cases, biopsy is recommended and, if the diagnosis is confirmed, appropriate breast cancer treatment begun.