Mastitis is an infection of the breast tissue associated with pain, swelling and redness of the breast. Most cases of mastitis happen in breastfeeding mothers, although it can also happen in women who are not breastfeeding. Mastitis can rarely occur in men. Inflammatory breast cancer has symptoms very similar to mastitis and must be ruled out. Women aged between 18 and 50 are the most commonly affected. Usually mastitis is an acute condition, which means it is a short period of inflammation. In rare cases, women have chronic mastitis, when it lasts a long time. Sometimes, the term 'chronic mastitis' is wrongly used to describe a condition in which the breasts are of an irregular rubbery consistency and contain painful or tender nodules or cysts, which feel lumpy.

Breast infections most commonly occur one to three months after the delivery of a baby, but they can occur in women who have not recently delivered as well as in women after menopause. Caused by the blocking of the milk ducts while the mother is lactating (see breastfeeding). It can cause painful areas on the breasts or nipples and may lead to a fever or flu-like symptoms. Mastitis can be discerned from simple blockages by the intensity of pain, heat emanating from the area, redness and fever in the mother. Signs of mastitis include part or all of the breast is intensely painful, hot, tender, red, and swollen. Some mothers can pinpoint a definite area of inflammation, while at other times the entire breast is tender. Cracked or bleeding nipples, stress or getting run down, missed feedings.

Treating mastitis usually requires a 10- to 14-day course of antibiotics. Massage and the application of heat can help prior to feeding. Avoid sleeping on your stomach or so far over on your side that your breasts are compressed against the mattress. After each feed, make sure your breast is empty and express any remaining milk if necessary. Breastfeed frequently. Try varying the position of the baby. Don't restrict the length of feedings. Acetaminophen and/or ibuprofen are safe to take while breastfeeding. Sleep without a bra. At other times, wear a looser fitting bra that does not put pressure on the affected area. Or if possible, go without a bra. Granulomatous mastitis has been treated with some success by a combination of steroids and Prolactin inhibiting medication.