What’s mastitis?

Reviewed by Leah DeShay

You can expect your breasts to become tender, swollen, and engorged when breastfeeding, especially within the first three to five days of your baby’s life. They’re adjusting to a surge of hormones, milk, and pressure, along with suckling or pumping. As you and your baby adjust to these many changes, you’ll want to be on the lookout for extra swelling, redness, warmth, or flu-like symptoms, which can signal a more serious condition, called mastitis.

What it is

Mastitis is a noncommunicable condition—marked by painful inflammation of the breast tissue in one or both breasts—when milk builds up in breast tissue or milk ducts become infected. An estimated 10 percent of breastfeeding mothers1 in the United States experience mastitis. If you have mastitis, you may notice tenderness, swelling, redness, and one or more lumps in your breasts that may feel hot to the touch. You may also experience flu-like symptoms, such as chills, fatigue, or a sudden fever above 101 degrees Fahrenheit. Less common symptoms include nausea, vomiting, and a yellowish discharge from the nipple that is not colostrum.

When it can occur

Mastitis is most likely to develop during the first 12 weeks of breastfeeding, when milk builds up in breast tissue or milk ducts become infected, but it can develop any time over the course of your breastfeeding journey.

What causes it

Mastitis is generally related to hyperlactation, which occurs when your breasts are producing a lot more milk than you are regularly removing from them by breastfeeding, hand-expressing, or pumping. Hyperlactation can lead to inflammation and plugged milk ducts, which refers to the clogged passageways that carry milk to the nipple. (Sometimes wearing a compressive bra or garment that is too tight, or doesn’t allow enough airflow to your breasts, can lead to a plugged milk duct.) And plugged milk ducts can commonly lead to mastitis infections.

Mastitis can also develop when bacteria becomes trapped in the breast tissue, either after entering the breast through a crack in the nipple skin (perhaps caused by an injury related to a poor latch) or after proliferating within the existing unremoved milk. Skin infections stemming from a badly fitting pump or other trauma to the nipple areola complex (NAC) can also contribute to mastitis.

What to do

If you suspect that you have mastitis, call your provider right away. It’s easier to treat when caught early. Treatment involves finding the underlying cause and decreasing inflammation, so your doctor may suggest that you take over-the-counter pain and inflammation relievers such as ibuprofen to ease discomfort. When inflammation progresses, it often leads to an infection that requires antibiotics. Meanwhile:

  • Continue breastfeeding your baby or pumping from both breasts.
  • Ask a lactation professional to teach you how to manage your supply while dealing with inflammation.
  • Apply warm or cool compresses such as chilled cabbage leaves, which can help reduce inflammation while providing pain relief.
  • Go braless to air out your breasts, when you can, and avoid tight garments on your breasts.
When to get help

If you are experiencing mastitis symptoms—especially a fever or other flu-oriented symptoms—immediately call your provider. And if you’re having any trouble breastfeeding while coping with mastitis, contact a lactation consultant for support.

In case you’re worried, you can’t spread mastitis to your baby: It’s not contagious. You can continue nursing or feeding your pumped milk.


1 https://www.aafp.org/pubs/afp/issues/2008/0915/p727.html#:~:text=Mastitis%20occurs%20in%20approximately%2010,and%20by%20optimizing%20breastfeeding%20technique.

Additional resources

What’s engorgement?

Breast engorgement is a common but uncomfortable condition when the breasts become swollen, tight, and sometimes warm to the touch.

What is breast edema?

Breast edema is the congestion of fluids in the interstitial tissue between milk ducts, typically before transitional milk comes in.

What are sore nipples?

Sore and sometimes painful nipples are so common at the start of breastfeeding that you can almost expect some discomfort.