Mastitis is inflammation of breast tissue that causes pain, swelling, and redness, most commonly during breastfeeding. It can occur with or without a bacterial infection, and symptoms often come on suddenly, including fever of 101°F (38.3°C) or higher. While lactational mastitis is the most familiar form, it can also develop in people who are not breastfeeding.
Types of Mastitis
Lactational mastitis is the most common type, developing during breastfeeding when milk builds up in the breast and triggers an inflammatory response. This doesn’t always mean bacteria are involved. In many cases, the inflammation itself is the problem, not an infection, and the distinction matters because treatment differs significantly depending on which is happening.
Nonlactational mastitis can affect anyone. One form, called periductal mastitis, involves inflammation of the ducts just behind the nipple. The cause is unknown. Another rare form, granulomatous mastitis, produces a chronic inflammatory reaction in breast tissue that can mimic other conditions. These types are less common but important to recognize because they don’t respond to the same approaches used for breastfeeding-related mastitis.
What Causes It
In breastfeeding, the most common trigger is milk that stays in the breast too long. When milk isn’t removed efficiently, it causes swelling and inflammation in the surrounding tissue. Cracked or sore nipples can also allow bacteria to enter, and the most common culprit is Staphylococcus aureus, a bacterium that lives on skin.
Overproduction of milk is a significant risk factor. When the breast makes more milk than the baby needs, the excess creates pressure and congestion in the ducts. This sets up conditions where inflammation can take hold and, in some cases, bacteria can overgrow. Improper pump flange sizes, excessive suction, or pumping for too long can also injure breast tissue and contribute to the problem.
Recognizing the Symptoms
Mastitis symptoms usually appear in one breast, though both can be affected. The hallmarks include:
- Breast tenderness, warmth, and swelling
- A painful or burning sensation that may be constant or worse during breastfeeding
- Skin redness in a wedge-shaped pattern spreading outward from the nipple (this can be harder to see on darker skin tones)
- A thickened area or lump in the breast
- Flu-like symptoms including fever, chills, body aches, and fatigue
The systemic symptoms are what often catch people off guard. Mastitis can make you feel genuinely sick, not just sore. The combination of a hot, red area on the breast with a sudden fever and body aches is the classic pattern.
How It’s Diagnosed
Mastitis is a clinical diagnosis, meaning your provider identifies it based on your symptoms and a physical exam. Lab tests and imaging are generally not needed. The exception is when a breast abscess is suspected, in which case an ultrasound can help determine whether a pocket of pus has formed and needs to be drained. About 5 to 11% of mastitis cases progress to an abscess, so most people won’t need imaging.
Treatment: What Actually Helps
Many mastitis symptoms resolve with conservative care, and current guidelines emphasize starting there rather than jumping straight to antibiotics. The approach depends on whether the mastitis is purely inflammatory or has progressed to a bacterial infection.
Conservative Care
Ice packs applied for 10 to 20 minutes every one to two hours while awake help reduce swelling and pain. Over-the-counter anti-inflammatory pain relievers like ibuprofen are a first-line recommendation, and they’re safe during breastfeeding. Heat should be used sparingly. A brief warm compress before feeding can help with milk flow, but prolonged heat can worsen swelling.
Continue breastfeeding on your baby’s cues, starting on the healthy breast for the next few days. If you’re pumping exclusively, pump enough for your baby but don’t try to “empty” the breast. This is a significant shift from older advice. Overfeeding from the affected breast or pumping aggressively to drain it perpetuates a cycle of overproduction that worsens tissue swelling and inflammation.
When Antibiotics Are Needed
Antibiotics are reserved for bacterial mastitis. Using them for purely inflammatory mastitis disrupts the natural microbial balance of the breast and can actually increase the risk of the condition worsening. When a bacterial infection is confirmed or strongly suspected (persistent high fever, worsening redness, no improvement after 24 to 48 hours of conservative care), a 10 to 14 day antibiotic course is typical.
Common Advice That Can Make Things Worse
Some of the most widely shared mastitis tips are now contradicted by current evidence. The Academy of Breastfeeding Medicine’s 2022 protocol update specifically warns against several popular remedies.
Deep breast massage, including using electric toothbrushes or vibrating devices, causes increased inflammation, tissue swelling, and small-vessel injury. If you want to use touch, light sweeping strokes along the skin surface (similar to lymphatic drainage) are the safer approach. Castor oil, saline soaks, and other topical products don’t treat mastitis because the inflammation is deep inside the breast tissue, not on the surface. These products may cause additional skin damage.
Nipple shields are another tool frequently suggested but not supported by evidence for mastitis. Like pumping, they represent a less efficient way to remove milk and can contribute to incomplete drainage. And contrary to what many people assume, mastitis is not caused by poor hygiene. Routine sterilization of pumps and household items is not necessary to prevent it, and excessive cleaning of the nipples can lead to skin breakdown and pain.
Prevention During Breastfeeding
The most effective prevention strategy centers on keeping milk production matched to your baby’s actual needs. Feed on demand rather than on a schedule, and avoid the temptation to pump extra milk “just in case.” Every additional pumping session signals your body to make more milk, and overproduction is one of the strongest risk factors for mastitis.
If you do use a pump, make sure the flange fits correctly, the suction isn’t too high, and you’re pumping at a frequency and volume that mimics what your baby would take. When you’re away from your baby, express just enough to stay comfortable rather than trying to fully drain both breasts.
Wearing a well-fitting supportive bra helps prevent fluid from pooling in breast tissue due to gravity. Lactating breasts have significantly increased blood flow, and unsupported tissue is more prone to swelling. If you’re producing more milk than your baby needs despite adjusting your pumping habits, hand expressing small volumes for comfort can help your supply gradually decrease to match demand. Persistent oversupply that doesn’t resolve on its own may need additional treatment from your provider.