by Alan R
(Breast Infection)


Mastitis is painful swelling and redness in the breast. It is most common among women who are breastfeeding. It usually occurs in one breast at a time, but it can occur in both breasts at the same time.

Mastitis can occur in women who are not breastfeeding. However, this fact sheet will focus on symptoms and treatment of mastitis that occurs with breastfeeding.

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Mastitis is often caused by breast milk trapped in a milk duct. The trapped breast milk can irritate the tissue around it and cause swelling and pain.

Mastitis can also be caused by bacteria. The bacteria can enter the breast through the milk duct or cracks in the skin of nipple. Once the bacteria enter the tissue, it can grow and cause an infection.

Risk Factors

Factors that may increase your chances of mastitis:

  • Previous mastitis
  • Abrasion or cracking of the breast nipple
  • Yeast infection of the breast
  • Pressure on the breasts, caused by:
    • Wearing a bra or clothing that is too tight
    • Sleeping on the stomach
    • Holding the breast too tightly during feeding
    • Baby sleeping on the breast
    • Exercising, especially running, without a support bra
    • Carrying a bag with a cross chest strap
  • Anything that causes too much milk to remain in the breast, including:
    • Irregular breastfeeding
    • Missed breastfeeding, which may cause swelling of the breast
    • Baby's teething
    • Use of supplemental bottle feeds
    • Incorrect positioning of the baby during feedings
    • Abrupt weaning


Mastitis may cause:

  • Redness, tenderness, or swelling of the breast
  • Fever
  • Fatigue
  • Aches, chills, or other flu-like symptoms
  • A burning feeling in the breast
  • A hard feeling or tender lump in the breast
  • Pus draining from the nipple


You will be asked about your symptoms and health history. A physical exam will be done. If the diagnosis is uncertain, or if mastitis recurs, your doctor may do:

  • Culture of breast milk or nipple discharge—to look for bacteria
  • Breast ultrasound —if a pocket of pus is suspected

Other conditions may cause similar symptoms. Your doctor may want to do tests to rule these out. Options may include:


Treatment may include:

Methods to Clear Blocked Breast Ducts

Pain and swelling can be caused by the blocked milk. Clearing the blockage can help. To clear blocked breast ducts try the following:

  • Breastfeed frequently.
    • Breastfeeding with mastitis is not harmful to the baby.
    • Talk to your doctor if you are also taking medicine. Some medicine can pass through breastmilk and harm the baby.
  • Offer the baby the inflamed breast first. This can encourage complete emptying of the breast.
  • Use a breast pump to express milk
  • Apply a warm compresses to breasts or taking a warm shower prior to feeding. It will stimulate milk ejection reflex.
  • Massage the inflamed breast before feeding
  • Position the baby so their chin points towards the blockage. This will encourage emptying of the blockage.

Pain Relief

To help reduce pain and swelling in the breast:

  • Apply ice compresses to the affected area of your breast after breastfeeding.
  • Consider using over-the-counter pain relievers. Ask your doctor which ones are safe.
    • Aspirin is not advised during pregnancy or breastfeeding.
  • Drink lots of fluids.
  • Get plenty of rest.

Infection Care

Antibiotics may be needed if there is an infection. They can cure it and reduce the risk of complications. Your doctor will recommend an antibiotic that is safe while breastfeeding.

An infection can sometimes lead to a pocket of pus. This pocket may not respond to antibiotics. It may need to be drained by the doctor.


To help reduce your chances of mastitis:

  • Breastfeed frequently.
  • Use a breast pump when you skip feedings.
  • Wash your hands and breast nipple before breastfeeding.
  • Avoid wearing bras or clothing that is too tight.
  • Avoid sleeping on your breasts, or allowing a baby to sleep on your breasts.
  • If your nipples crack, apply lotion or cream as advised by your doctor.


Office on Women's Health 

The American Congress of Obstetricians and Gynecologists 


Canadian Women's Health Network 

Society of Obstetricians and Gynaecologists of Canada 


Amir L. Breastfeeding and Staphylococcus aureus: Three case reports. Breastfeed Rev. 2002;10(1):15-18.

Barbosa-Cesnik C, Schwartz K, Foxman B. Lactation mastitis. JAMA. 2003;289(13):1609-1612.

Laibl VR, Sheffield JS, Roberts S, McIntire DD, Trevino S, Wendel GD Jr. Clinical presentation of community-acquired methicillin-resistant Staphylococcus aureus in pregnancy. Obstet Gynecol. 2005;106(3):461-465.

Mastitis. Family Doctor—American Academy of Family Physicians website. Available at: Updated April 1, 2014. Accessed April 17, 2018.

Masitis. EBSCO DynaMed website. Available at:  . Updated March 15, 2016. Accessed April 17, 2018.

Spencer J. Management of mastitis in breastfeeding women. Am Fam Physician. 2008;78(6):727-731.

11/5/2014 DynaMed's Systematic Literature Surveillance  : Amir L, The Academy of Breastfeeding Medicine Protocol Committee. ABM clinical protocol #4: mastitis, revised March 2014. Breastfeed Med. 2014;9(5):239-243.

Revision Information

  • Reviewer: EBSCO Medical Review Board Marcie L. Sidman, MD
  • Review Date: 03/2018
  • Update Date: 07/12/2018