A breast infection, medically called mastitis, is inflammation of breast tissue that often involves a bacterial infection. It causes pain, swelling, and redness in the affected breast, sometimes alongside fever and flu-like symptoms. While most common during breastfeeding, breast infections can happen to anyone, including people who aren’t lactating and, rarely, men.
Lactational vs. Non-Lactational Infections
There are two broad categories of breast infection, and they differ in who they affect, why they happen, and how they’re treated.
Lactational mastitis develops during breastfeeding, usually when milk doesn’t drain fully from the breast. A clogged duct creates a buildup of milk that becomes a breeding ground for bacteria. This type accounts for the majority of breast infections and most often shows up in the first few weeks of nursing, though it can occur at any point during lactation. Milder cases sometimes resolve with frequent feeding and self-care measures alone, without antibiotics.
Non-lactational mastitis occurs in people who aren’t breastfeeding. It typically involves compression or blockage of the milk ducts and swelling of surrounding tissue. Unlike its breastfeeding-related counterpart, non-lactational mastitis almost always requires some form of medical treatment. One specific type, called periductal mastitis, tends to develop around the ducts behind the nipple and has its own distinct set of risk factors.
What Causes Breast Infections
The bacteria responsible for breast infections are, in most cases, the same ones that normally live on your skin. Staphylococcus aureus is the single most common culprit. Notably, the majority of Staph aureus found in breast infections is now the antibiotic-resistant form, MRSA, which can influence treatment decisions.
Up to 40% of breast abscesses involve more than one type of bacteria, including a mix of organisms that thrive with and without oxygen. This is one reason that cultures (where a sample is tested to identify the specific bacteria) can be important for guiding treatment, especially when a first round of antibiotics doesn’t work.
Several factors increase your risk:
- Cracked or sore nipples, which give bacteria a direct entry point into breast tissue
- Nipple piercings, which create a permanent opening in the skin
- Smoking, a well-established risk factor, particularly for periductal mastitis in non-breastfeeding individuals
- Tight-fitting bras or innerwear that compress the breast and restrict drainage
- Poor hygiene around the nipple area
- Incomplete milk drainage during breastfeeding, whether from a weak latch, skipped feedings, or sudden weaning
How a Breast Infection Feels
A breast infection typically affects one breast, not both. The hallmark is a firm, swollen, painful area that feels warm to the touch, often with visible redness spreading across the skin. In breastfeeding women, this redness sometimes appears in a wedge-shaped pattern radiating outward from the nipple.
What catches many people off guard is how sick a breast infection can make you feel beyond the breast itself. Fever of 100.4°F (38°C) or higher, chills, body aches, rapid heart rate, and a general sense of exhaustion are all common. Many describe it as feeling like the flu hit them suddenly. These whole-body symptoms can actually appear before the breast itself becomes noticeably red or swollen, which sometimes delays recognition.
A less common type called idiopathic granulomatous mastitis has a somewhat different presentation: a tender mass that can occur in almost any part of the breast, along with nipple discharge, skin ulcers, and swollen lymph nodes under the arm. About 34% of people with this form also develop symptoms outside the breast, including joint pain, joint swelling, and red, tender nodules on the lower legs.
When an Infection Becomes an Abscess
The most common complication of a breast infection is an abscess, a walled-off pocket of pus within the breast tissue. An abscess typically feels like a distinct, painful lump that may feel fluid-filled. The overlying skin can become taut and shiny, and pain often intensifies rather than responding to antibiotics.
Abscesses need to be drained, not just treated with medication. This is usually done with a needle guided by ultrasound or, for larger collections, through a small incision. The fluid is often sent for testing to identify which bacteria are involved, since up to 40% of abscesses contain multiple types of organisms. Recovery after drainage is generally straightforward, though some abscesses refill and need repeat drainage.
Stopping breastfeeding suddenly during a breast infection actually raises your risk of abscess formation. Even if nursing is uncomfortable, continuing to empty the breast helps prevent pus from accumulating.
Treatment and What to Expect
For breastfeeding-related mastitis, the first line of treatment combines frequent breastfeeding or pumping (starting on the affected side) with oral antibiotics when symptoms include fever or aren’t improving. Antibiotic choice is ideally guided by culture results or local resistance patterns, which matters because of the high prevalence of MRSA in breast infections. Most people can be treated entirely at home. Hospital admission and IV antibiotics are reserved for severe cases, such as signs of sepsis or inability to keep oral fluids down.
You should start feeling better within two to three days of beginning antibiotics, though it’s important to finish the full course even once symptoms improve. If you’re not improving in that window, your provider may want to check for an abscess with ultrasound or reconsider the antibiotic choice.
Non-lactational mastitis follows a similar antibiotic approach but tends to be more stubborn. Recurrence is common, particularly with periductal mastitis, and some people need repeated courses of treatment or minor procedures to address underlying duct problems.
Breastfeeding During an Infection
One of the most common concerns is whether it’s safe to keep nursing. The answer is clear: there is no evidence of risk to a healthy, full-term infant from breastfeeding during mastitis. Both the American Academy of Pediatrics and the World Health Organization recommend continuing breastfeeding through a breast infection. In fact, breastfeeding helps clear the infection by keeping milk moving through the ducts.
If your baby refuses the affected breast, which sometimes happens because milk volume drops or the taste changes during inflammation, express the milk by hand or with a pump. Keeping the breast empty is one of the most important things you can do to prevent the infection from worsening. Sudden weaning during active mastitis is one of the clearest paths to abscess development.
Ruling Out Other Conditions
Most breast infections are straightforward to diagnose based on symptoms alone. However, a breast infection that doesn’t improve with antibiotics raises a red flag for inflammatory breast cancer, a rare but aggressive form of cancer that can look remarkably similar to mastitis. Both cause redness, swelling, warmth, and skin changes.
On ultrasound, inflammatory breast cancer tends to show increased blood flow within the tissue, specific dense areas with shadowing, and a more chaotic tissue pattern than a typical infection. Lymph nodes under the arm also look different: in a simple infection, swollen lymph nodes maintain their normal internal structure, while cancerous lymph nodes show irregular thickening and loss of their normal architecture. If your symptoms persist after a full course of antibiotics, imaging and possibly a biopsy are the appropriate next steps.
Prevention Strategies
For breastfeeding women, the most effective prevention comes down to keeping milk flowing. Feed frequently, ensure a good latch, and avoid long stretches without emptying the breast. Tight clothing that compresses breast tissue should be avoided, and cracked nipples deserve prompt attention since they’re a direct entry point for bacteria.
There’s emerging evidence that probiotics may help. A Cochrane review found that probiotics roughly halved the risk of mastitis compared to placebo, though the certainty of this evidence is rated low, partly because data from the largest trial was withheld due to a contractual agreement with the probiotic manufacturer. Breast massage techniques also show promise: one trial of 300 women found that breast massage combined with low-frequency pulse treatment reduced mastitis risk substantially compared to routine care.
For non-lactating individuals, the most impactful preventive step is quitting smoking, which is strongly linked to periductal mastitis. Keeping nipple piercings clean, or removing them if infections recur, also reduces risk.