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What are the signs of mastitis?

Mastitis usually causes a sore, red, swollen, hot area on one breast, sometimes with a lump, plus flu-like symptoms such as fever, chills, and body aches.

Symptoms often come on quickly and can include nipple discharge or pain that worsens during feeding.

Strength of evidence

Good

Based on consistent descriptions from national health guidance and clinical review articles rather than randomized trials, since mastitis is diagnosed by symptoms, not tested in trials.

What the evidence says

Mastitis typically affects only one breast and comes on fairly suddenly. Look for a swollen, sore, or hot area on the breast, which may look red (though redness can be harder to see on darker skin tones), or a firm, wedge-shaped lump.

You might also notice burning pain in the breast, either constant or only while breastfeeding, and nipple discharge that can be white or streaked with blood.

Many people also get flu-like symptoms alongside the breast changes, such as fever, chills, tiredness, and body aches. These general symptoms, combined with the breast changes, are what usually point to mastitis rather than just a blocked duct.

If you notice these signs, keep breastfeeding or expressing milk from the affected side if possible, and contact your doctor or midwife, especially if fever is high or symptoms are getting worse quickly.

Sources

✓Reviewed by CH, MD, FRCPC

Reviewed by a specialist physician certified by the Royal College of Physicians and Surgeons of Canada, who has read this answer against the sources listed above and confirmed it reflects them. That is not medical advice about your child. How we review

Answer checked July 29, 2026

Educational information only. Not medical advice, not a diagnosis, and no doctor-patient relationship is created by using this. Founded Parent has not examined your child and does not know their history, so this may not apply to you. In an emergency, call your local emergency number. What Founded Parent cannot do

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