Mastitis While Breastfeeding: Symptoms, Treatment, and When to Call Your Doctor

You wake up feeling like you have the flu — achy, feverish, exhausted — and one of your breasts is red, hard, and sore to the touch. It is an unsettling combination, especially when you have a newborn to care for. What you are most likely dealing with is mastitis.

Mastitis is common, it is treatable, and it does not mean you have to stop breastfeeding. Here is what the AAP, the Cleveland Clinic, and researchers at the NIH actually say — along with practical guidance on what to do when it happens.

01What mastitis is

Mastitis is an inflammation of the breast that can — but does not always — involve a bacterial infection. According to the Cleveland Clinic, it affects up to 10% of breastfeeding women in the United States, with some global studies putting the figure higher. The NIH's StatPearls database notes that incidence estimates range from 1% to 33% globally, with most cases occurring within the first six weeks postpartum — though it can appear at any point during breastfeeding.

There are two stages. Inflammatory mastitis starts without a bacterial infection: milk has pooled somewhere in the breast, the surrounding tissue becomes inflamed, and the breast swells and reddens. If that milk stasis is not resolved quickly, bacteria can enter — often through a cracked or sore nipple — and a full bacterial infection takes hold. Both stages feel similar, which is why it is important to start treatment early rather than waiting to see how bad it gets.

02What it feels like

The AAP's HealthyChildren.org describes the breast symptoms as "swelling, warmth, burning, redness or pain" in one area of the breast. The Cleveland Clinic adds that you may feel a hard lump and a burning sensation that gets worse during nursing.

What catches many parents off guard is that mastitis often also causes systemic, flu-like symptoms. The NIH StatPearls article lists fever of 100.4°F (38°C) or higher, chills, body aches, and fatigue as common. If you suddenly feel like you have been hit by a truck and one breast looks angry, mastitis is the most likely explanation.

03Why it happens

The root cause of most cases is milk stasis — milk that is not being fully removed from the breast. A 2020 review published in the NIH's PubMed Central lists the main contributors:

• Going too long between feedings or cutting feeds short before the breast is well-drained
• A poor latch that keeps your baby from drawing milk out effectively
• Engorgement from a sudden oversupply or a missed feeding
• Rapid weaning, which reduces how often the breast is emptied
• Tight bras or clothing that press on the breast and restrict a duct
• A cracked or sore nipple, which can let bacteria in and cause feeds to be cut short
• Tongue tie in your baby, which affects how well they can latch and drain the breast

The NIH StatPearls article notes that the bacteria most often responsible when an infection does develop are Staphylococcus and Streptococcus species — the same bacteria commonly found on skin. They get in through a nipple wound and thrive in pooled milk.

04What to do first — before you see a doctor

The AAP recommends starting with supportive care: rest, plenty of fluids, and ibuprofen or another anti-inflammatory pain reliever. The Cleveland Clinic adds applying an ice pack while lying back to help with swelling. The PMC review notes that ibuprofen up to 1,600 mg per day is commonly used in breastfeeding mothers for pain and inflammation.

The most important home step, though, is keeping the affected breast well-drained. The AAP is explicit: continue breastfeeding or pumping, even on the painful side. Stopping feeds causes more milk to back up, which makes the inflammation worse — and the PMC review notes that premature breastfeeding cessation is itself one of the complications of untreated or undertreated mastitis.

05When to call your doctor

The AAP says to contact your provider right away if symptoms appear, and sooner rather than later if things are getting worse. The Cleveland Clinic recommends calling if at-home care has not helped within 24 hours, or if you develop new symptoms like a lump that was not there before, discharge from the nipple, or worsening redness spreading beyond the original area.

Most doctors will prescribe antibiotics if your symptoms have not clearly improved within 24 hours or if you have a fever. The PMC review notes that common options include cephalexin and dicloxacillin, effective against the bacteria most likely responsible. The typical course is 10 to 14 days. One important note from the AAP: complete the entire antibiotic course. Stopping early because you feel better increases the risk of reinfection and scarring that could affect milk production.

06Is it safe to keep breastfeeding?

Yes. The AAP is direct on this: your baby will not be harmed by milk from the affected breast, even if a bacterial infection is present. The antibiotics most commonly prescribed for mastitis are generally considered safe for nursing infants.

If the pain on the infected side is too severe to nurse, you can pump to keep that side empty and feed your baby on the other breast in the meantime. The AAP notes this is a reasonable short-term approach — the key is not leaving the breast full. If a latch issue or tongue tie is contributing, this is a good time to contact a lactation consultant; see the guide to newborn tongue tie for more on that.

07How long until you feel better

The Cleveland Clinic says that with proper treatment, symptoms should improve dramatically within 48 to 72 hours and inflammatory mastitis typically resolves within 10 to 14 days. Most people feel noticeably better within a couple of days of starting antibiotics — though the course needs to be completed in full regardless.

Recurrence is possible. The NIH StatPearls database notes that 6.5% to 8.5% of women who have had mastitis once will have it again. If you have repeated episodes, it is worth working with a lactation consultant to look at your feeding patterns, latch, and bra fit.

08How to reduce the risk of it happening again

The NIH StatPearls article and the PMC review agree on the same core prevention strategies:

• Empty the breast fully at every feed. Milk that sits is the main risk factor. If your baby does not drain one side, pump the remainder.
• Vary your feeding position. Different positions drain different parts of the breast and can help prevent one area from consistently staying full.
• Address nipple damage quickly. A cracked nipple is a route for bacteria. A lactation consultant can assess latch and help. Our guide to newborn feeding schedules covers early feeding patterns that keep the breast well-drained.
• Avoid tight bras and underwire. Constant pressure on a duct is a setup for milk stasis.
• Do not wean too fast. Rapid drops in feeding frequency leave milk sitting in the breast. If you are weaning, do it gradually.
• Do not pump more than necessary. Overpumping signals your body to make more milk than your baby needs, which increases the engorgement risk. The Cleveland Clinic notes this as an explicit prevention tip.

09The short version

Mastitis is painful and can come on fast, but it responds well to treatment when caught early. Rest, drain the breast, take ibuprofen, and call your provider if you are not improving within 24 hours. Keep breastfeeding — it is safe for your baby and good for your recovery. If you are in the thick of the early weeks and feeling overwhelmed, the newborn basics guide has the fundamentals in one place, and night help exists for exactly the moments when you need another set of hands.

Questions parents actually ask

Newborn Weeks is planning help, not medical advice — always follow your own doctor, midwife, or pediatrician.