What causes mastitis

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Last updated: April 4, 2026

Quick Answer: Mastitis is most commonly caused by bacteria entering the breast tissue, usually through a crack or break in the skin of the nipple. This can happen during breastfeeding due to improper latch or if milk becomes stagnant in the breast, creating a breeding ground for bacteria.

Key Facts

What Causes Mastitis?

Mastitis is an inflammation of the breast tissue that can cause pain, swelling, warmth, redness, and sometimes flu-like symptoms. While it can occur in anyone, it is most common in breastfeeding women, often referred to as lactation mastitis. Understanding the causes is crucial for prevention and effective treatment.

Primary Cause: Bacterial Infection

The most frequent culprit behind mastitis is the invasion of bacteria into the breast tissue. The most common bacterium identified is Staphylococcus aureus, which is often present on the skin and in the nose of healthy individuals. These bacteria can enter the breast through various means:

Entry Points for Bacteria

1. Cracked or Damaged Nipples: During breastfeeding, the delicate skin of the nipple can develop small cracks, fissures, or sores. These breaks in the skin create an easy pathway for bacteria to enter the milk ducts and surrounding breast tissue. Factors contributing to nipple damage include an improper latch by the baby, incorrect positioning, or aggressive nipple care.

2. Milk Stasis (Blocked Milk Ducts): When milk is not effectively removed from the breast, it can become stagnant. This 'milk stasis' creates an ideal environment for bacteria to multiply. Blocked ducts can occur for several reasons, including:

Other Contributing Factors

While bacterial infection and milk stasis are the primary drivers, several other factors can increase a woman's susceptibility to mastitis:

Non-Lactational Mastitis

It's important to note that mastitis can also occur in women who are not breastfeeding. This is often called non-lactational mastitis or periductal mastitis. It is more commonly associated with conditions like:

In summary, mastitis is predominantly an infection that arises when bacteria enter the breast tissue, often facilitated by a blocked milk duct or damage to the nipple. Maintaining good breastfeeding practices, managing stress, and addressing any nipple issues promptly are key preventative measures.

Sources

  1. Mastitis - Symptoms and causes - Mayo Clinicfair-use
  2. Mastitis - NHSfair-use
  3. Mastitis - Breastfeeding - CDCfair-use

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