Mastitis is inflammation of the breast, sometimes with a bacterial infection. It usually shows up as a hot, painful, swollen area in one breast, often with flu-like symptoms such as fever, chills or aches. The approach to treating it has changed: the Academy of Breastfeeding Medicine's 2022 protocol recommends feeding normally rather than trying to empty the breast, cold packs and anti-inflammatory pain relief, and no deep massage.

Most cases improve with self-care. See a doctor if you're not starting to improve within 12 to 24 hours, or sooner if you feel very unwell — and call your local emergency number (000 in Australia, 999 in the UK, 911 in the US) if you have signs of sepsis. This guide explains the spectrum from "blocked duct" to mastitis, what to do and what to avoid, and how to tell when it's urgent.

What is mastitis, and what is a blocked duct?

Breast inflammation is now seen as a spectrum rather than separate problems. The Academy of Breastfeeding Medicine (ABM) describes it running from engorgement and "blocked ducts" through inflammatory mastitis to bacterial mastitis and, less often, an abscess.

  • "Blocked duct" (localised inflammation). The Australian Breastfeeding Association's page on localised breast inflammation explains this is inflammation in the breast tissue, not something physically blocking a duct. The ABM says the ducts are tiny and interlacing, so a single "plug" of milk isn't possible. It shows up as a firm lump or swollen, lumpy area, sometimes red, that's tender — often most when milk starts to flow — without fever.
  • Inflammatory mastitis. The area becomes redder, more swollen and painful, and you feel unwell, with fever, chills or a fast heart rate. The ABM points out this can happen without any infection.
  • Bacterial mastitis. Inflammation progresses to an infection that needs antibiotics.
  • Abscess. A collection of pus that needs draining. The ABM says about 3% to 11% of people with acute mastitis develop one.

Lactating breasts can feel lumpy and even sore at times without anything being wrong. The ABM also notes that hot flushes and sweats are common after birth and can feel like a fever.

What are the symptoms of mastitis?

The NHS mastitis page and the Australian Breastfeeding Association's mastitis page describe:

  • a swollen, hot, painful area, often wedge-shaped or a hard lump, usually in one breast
  • redness, or skin that looks darker, shiny or streaked — redness can be harder to see on black or brown skin
  • burning pain, all the time or only while feeding
  • nipple discharge, which may be white or streaked with blood
  • flu-like symptoms: aches, fever, chills or shivers, and tiredness
  • feeling unwell, which can be the first sign. Mastitis can come on quickly.

What causes mastitis?

The Australian Breastfeeding Association lists things that make inflammation more likely:

  • longer gaps between feeds, including when your baby starts sleeping longer
  • rushed feeds or a baby who isn't removing milk well, for example because of attachment
  • oversupply
  • pressure on the breast from a tight bra, clothing or sleeping position
  • damaged nipples.

The ABM adds that overfeeding from one side, "pumping to empty" and deep massage can make inflammation worse rather than better.

How do you treat mastitis at home?

These steps combine the ABM protocol, the NHS and the Australian Breastfeeding Association.

  1. Keep breastfeeding as your baby needs. Feed when your baby wants, and offer a feed if your breasts feel uncomfortably full. Don't stop suddenly. Your milk is safe for your baby.
  2. Don't try to empty the breast. The ABM says overfeeding from the affected side or "pumping to empty" keeps milk production high and worsens swelling and inflammation. Express only enough to feel comfortable, and only the amount your baby would take if you're separated.
  3. Use cold. Put a covered cold pack on the sore area between feeds. The NHS suggests 10 minutes every hour; the ABM says ice can be used hourly or more often if you like.
  4. Take anti-inflammatory pain relief. The NHS says paracetamol or ibuprofen can help with pain and fever, and to avoid aspirin. Ask your pharmacist or doctor which is right for you and follow the label for doses.
  5. Touch gently. The ABM recommends light, sweeping strokes over the skin (like lymphatic drainage) rather than deep massage. The Australian Breastfeeding Association describes gentle stroking towards the nipple before feeds.
  6. Check attachment. A midwife, child-health nurse or lactation consultant can watch a feed — see latch and positioning.
  7. Wear a supportive, comfortable bra and avoid tight clothing on the area.
  8. Rest, drink to thirst and eat well. Ask for help with your baby and the house.

If the area right behind the nipple is so swollen that no milk comes out, the ABM says you can feed from the other breast for a while and go back to the sore side once the swelling settles.

What about warmth?

Sources differ slightly. The Australian Breastfeeding Association and healthdirect in Australia suggest brief warmth only just before a feed to help let-down, because warmth at other times can worsen inflammation. The ABM notes heat may worsen swelling but can be comforting for some people. Either way, cold between feeds is the main treatment.

What should you avoid with mastitis?

The ABM protocol advises against several older or popular remedies:

  • Deep or firm massage, including with electric toothbrushes or vibrating devices. It increases inflammation and tissue damage, and can contribute to a more serious collection forming.
  • Pumping or feeding extra to "empty" the breast. This drives oversupply and keeps the cycle going.
  • Squeezing or trying to push out a "plug".
  • Saline soaks, castor oil, Epsom salts and other topical products.
  • Nipple shields, unless a lactation consultant has advised one for another reason.
  • Opening or picking at a white spot (bleb) on the nipple — this causes more trauma.
  • Cabbage leaves instead of cold packs. The ABM says they work no better than ice and can carry Listeria bacteria.

The NHS also says to avoid firm pressure on the breast and oils, soaks or creams.

When is mastitis an emergency?

The NHS sepsis page lists these as reasons to call an ambulance, and notes that having given birth in the past 6 weeks raises the risk.

See a doctor the same day if:

  • you feel very unwell, with fever, chills or flu-like aches — don't wait out the 12 to 24 hours
  • redness is spreading or forming streaks, or pain is getting rapidly worse
  • you can feel a firm, swollen area that isn't going down, which may need an ultrasound to check for an abscess.

See a doctor soon (within a day or so) if:

  • symptoms haven't started to improve 12 to 24 hours after self-care — the NHS, the Australian Breastfeeding Association and healthdirect all use this timeframe
  • you're not better 48 hours after starting antibiotics, according to the NHS
  • you have mastitis and aren't breastfeeding.

Mention it at your next appointment, or ask for a review, if mastitis keeps coming back. The ABM advises a milk culture for repeated infections, and imaging if it keeps recurring in the same spot or a lump remains after the inflammation settles. A lactation consultant or a breastfeeding helpline (the Australian Breastfeeding Association on 1800 686 268 in Australia, the National Breastfeeding Helpline on 0300 100 0212 in the UK) can help with feeding patterns and oversupply.

Can you keep breastfeeding with mastitis?

Yes. The NHS, the Australian Breastfeeding Association and the ABM all say your milk is safe for your baby, including during bacterial mastitis. The ABM says bacterial mastitis isn't contagious, doesn't need sterilising of pump parts, and doesn't mean you should express and throw milk away.

If you're prescribed antibiotics, the NHS says a very small amount may pass into your milk; there's no risk to your baby, though it might make them a little unsettled. The Australian Breastfeeding Association suggests telling your doctor if you've had thrush after antibiotics before.

Mastitis is painful and draining, and it can knock your confidence. The ABM notes that anxiety and low mood are more common when breastfeeding is hard. If you're feeling flat or anxious, talk to your GP or call a perinatal support line (PANDA on 1300 726 306 in Australia, Samaritans on 116 123 in the UK, the National Maternal Mental Health Hotline on 1-833-852-6262 in the US); see postnatal mood.

What's useful to note

Write down when symptoms started, your temperature readings, which breast and where, what you've tried and when, and any medicine you've taken. If it comes back, note any patterns — such as longer gaps between feeds or a tight bra — to discuss with your doctor or lactation consultant.