What Is Mastitis?

You’re feeding your baby, things are just settling down — and then one breast turns sore, hot, and tender, and you start to feel almost flu-like. Is it serious? Should you stop feeding? Do you need to be seen today? Mastitis raises all of those questions at once, so this article answers them in the order most people ask them. The video at the top of this page, "Mastitis", runs just under four minutes; its own description defines mastitis as inflammation of the tissue in one or both mammary glands inside the breast, notes that it usually affects women who are breastfeeding — which is why it’s often called lactation mastitis — and describes the patient feeling a hard, sore spot inside the breast.

What is actually inflamed?

Put simply, the breast tissue itself becomes inflamed. In breastfeeding, that usually starts when milk isn’t draining well from part of the breast — a duct becomes blocked, milk builds up behind it, and the surrounding tissue gets sore and swollen. Bacteria can then get in, often through a sore or cracked nipple, and turn inflammation into infection. That’s the pattern behind the hard, sore spot the anchor video describes. Mastitis is overwhelmingly a breastfeeding problem, but it isn’t only one: breast inflammation can occasionally occur outside breastfeeding too, and any new breast lump or skin change at any stage deserves the same careful check you’d give it while nursing — learning what your breasts normally feel like, as our guide to breast self-examination explains, makes changes easier to spot.

How is that different from a clogged duct?

This is the question almost everyone asks first, because the two feel similar at the start. A clogged duct tends to stay local: one tender lump or sore patch, sometimes a little redness over it, while you otherwise feel well. Mastitis spreads the picture out — the red, warm area is wider, the pain is stronger, and crucially you feel unwell in yourself, with feverish, achy, flu-like symptoms. A useful way to think about it is that a blocked duct is a plumbing problem in one small area, while mastitis is that problem plus inflammation — and often infection — in the tissue around it. A clogged duct that isn’t clearing is worth attention precisely because it can tip over into mastitis.

What happens when you get checked?

Expect questions before anything else: when the soreness started, whether you have a fever, how feeding is going, and whether the nipple is cracked or sore. Then the clinician examines the breast, feeling for the tender area and looking at how far the redness extends. For straightforward mastitis, that history and examination are usually enough to make the diagnosis — there’s no single test that "proves" it. Imaging enters the picture when something doesn’t fit the simple story, or when an abscess is suspected. If you’re at an age or stage where a breast lump needs imaging in its own right, our article on what a mammogram is and how it is done explains what that examination involves.

Can you keep breastfeeding, and what helps?

In most cases, yes — and keeping the milk moving is generally part of the answer rather than part of the problem, because a breast that keeps draining is less likely to stay congested. Feeding or expressing from the sore side, resting when you can, and drinking enough fluids are the everyday measures clinicians usually start with, alongside whatever pain relief your own clinician advises for you. When infection is likely — spreading redness, fever, feeling properly unwell, or no improvement — antibiotics are commonly prescribed; which one, and for how long, is a decision for the clinician who has examined you. What matters most is the direction of travel: mastitis that’s settling can be watched, while mastitis that’s worsening, or not improving after a day or so of care, needs to be seen again promptly rather than waited out.

What if it turns into an abscess?

Occasionally, instead of clearing, an infected area collects into a pocket of pus called a breast abscess. It tends to announce itself as a painful, swollen lump that doesn’t settle even as the wider redness improves. An abscess generally needs the pus drained, not just medicine — the second video on this page, "Breast Abscess Drainage" (7 minutes 45 seconds), shows that drainage procedure, and its description makes the same link: breast abscesses are often linked to mastitis and usually affect women who are breastfeeding. An abscess is uncommon, and it’s a reason for prompt review, not panic — but a lump that stays painful and swollen after mastitis treatment is exactly the kind of finding to take back to your clinician quickly.

Frequently Asked Questions

Is mastitis an infection or just inflammation?

It can be either, and it often starts as one and becomes the other. Blocked drainage and milk build-up cause inflammation first; if bacteria get in, infection follows. That’s why early mastitis is sometimes managed with drainage and simple measures, while mastitis with fever and spreading redness is more likely to be treated as an infection.

Can I keep breastfeeding with mastitis?

Usually, yes. Keeping milk moving out of the affected breast is generally encouraged, because it helps the congestion clear. If feeding from that side is too painful, expressing milk can keep drainage going. Your clinician can advise on your specific situation, especially if you have been prescribed medication.

How quickly should mastitis improve?

With drainage, rest, and treatment where it’s needed, the feverish, unwell feeling and the soreness usually start easing first, with the red patch fading more slowly. If things are getting worse instead — more pain, more redness, a new swollen lump, or a fever that won’t settle — get reviewed again promptly rather than waiting.

Can mastitis happen if I’m not breastfeeding?

It can, though it’s much less common. Breast inflammation outside breastfeeding still needs a proper examination, because a clinician will want to check the lump or skin change itself and not simply assume mastitis. Any new, persistent breast change is worth having assessed in person.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about mastitis, not medical advice and not a diagnosis. Breast pain with fever, spreading redness, or a lump that isn’t settling should be assessed promptly by a clinician, who can examine you directly.