Mastitis is an infection in the breast. It most commonly affects women who are breastfeeding, but less often it affects women who are not breastfeeding.

A clogged milk duct, not fully draining milk from the breast, or breaks in the skin of the nipple can lead to infection. This causes the body’s white blood cells to release substances to fight the infection, which can lead to swelling and increased blood flow. The infected part of the breast may become swollen, painful, red, and warm to the touch. The woman may also have fever and a headache, or general flu-like symptoms.


Mastitis can usually be diagnosed based on a woman’s symptoms and the results of a breast exam. It usually affects only one breast.


Mastitis is treated with antibiotics. In some cases, a breast abscess (a collection of pus) may form. Abscesses are treated by draining the pus, either by surgery or by using a needle (often guided by ultrasound), and then antibiotics. 

Inflammatory breast cancer has symptoms that are a lot like mastitis and can be mistaken for an infection. If you’ve been diagnosed with mastitis and antibiotic treatment doesn’t help within a week or so, you might need a skin biopsy to be sure it’s not cancer. Inflammatory breast cancer can spread quickly, so don’t put off going back to the doctor if you still have symptoms after antibiotic treatment.

How does mastitis affect your risk for breast cancer?

Having mastitis does not raise your risk of developing breast cancer.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Schnitt SJ, Collins LC. Pathology of benign breast disorders. In: Harris JR, Lippman ME, Morrow M, Osborne CK, eds. Diseases of the Breast. 4th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2010:69-85.

Last Medical Review: March 16, 2015 Last Revised: April 21, 2016

American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.