What Really Happens Inside Your Breast When You Get Mastitis?
In 2022, the Academy of Breastfeeding Medicine (ABM) released Clinical Protocol #36, a major update on how healthcare providers manage the mastitis spectrum. This new protocol was developed after new technology completely changed how we view the anatomy of the breast. It also revolutionised the treatment of engorgement, mastitis, breast abscesses, and plugged ducts.
This protocol is still new — many doctors, nurses, and even lactation consultants may not yet be aware of it. Unless they’ve kept up with the latest breastfeeding research, they may still follow outdated practices.
You can access the full protocol here. It’s a good idea to take a copy with you to your next appointment to ensure that you receive the correct treatment.
Before you proceed…
This is a fairly complicated and technical read, and is aimed at the mom who wants ALL the information. If you’re not interested in so much detail and just want to get rid of the problem, read our feature on treating engorgement and mastitis.
Understanding the Mastitis Spectrum
Previously, engorgement was seen as simply “too much milk” and mastitis as a bacterial infection. We now know these related conditions .
We now know that it’s not so simple, and that these conditions are part of a whole range of symptoms linked to inflammation in the breast. Mostly, one thing leads to another.
🔹 Engorgement
Engorgement is swelling or fullness in the breast. It can be a symptom of mastitis or a standalone condition.
- Primary engorgement occurs a few days after birth when milk “comes in.” It’s normal but should be managed correctly to avoid complications.
- Secondary engorgement happens later — usually due to skipped feeds, poor latching, or an interruption in milk drainage. Read more on what causes engorgement and mastitis
Read more on the risk factors for mastitis
🔹 Mastitis
Mastitis refers to inflammation of breast tissue. Incorrectly managed engorgement can progress to mastitis.
There are several types:
- Inflammatory mastitis – inflammation without infection (no antibiotics needed).
- Bacterial mastitis – where bacteria infect the inflamed area.
- Subacute mastitis – lingering symptoms like burning pain or blockages even after antibiotics.
Read more on the treatment of engorgement and mastitis.
🔹 Abscesses and Galactoceles
When bacterial mastitis is left untreated or treated incorrectly, it can form a breast abscess — a painful pocket of pus and milk that usually requires drainage.
A galactocele is a milk-filled cyst caused by a narrowed duct. It may be harmless or, if infected, can also progress to an abscess.
Inside the Breast: Why Old Treatments Can Be Harmful
Modern ultrasound studies have shown that the breast is far more complex than we once thought.
- Milk ducts are microscopic and interlacing network, not large tubes that can simply “get blocked.”
- The breast has a rich blood supply and fine muscle walls that respond to inflammation and pressure.
This means that heat and aggressive breast massage can worsen inflammation and tissue damage — a key reason the new protocol discourages it.
See Medela’s anatomy fact sheet for more insights.
What Causes Mastitis Spectrum Conditions?
Two major factors drive most breast complications:
- Hyperlactation (Oversupply)
When the breast produces more milk than baby needs or is not emptied effectively, pressure builds.
This can result from:
- Excessive pumping
- Scheduled feeds instead of on-demand feeding
- Latch problems
- Using medications or supplements to increase supply unnecessarily
- Dysbiosis (Microbial Imbalance)
There are millions and millions of micro-organisms in the human body, many of them present in breast milk and the milk ducts. These good bacteria are essential for proper immune functioning.
When there is an imbalance, it creates a biofilm that clings to the side of the milk ducts (think of algae growing against the side of a swimming pool). This narrows the milk ducts and obstructs milk flow, which causes inflammation. Milk is squeezed from the milk ducts into the tissue in-between ducts and glands.
Eventually the lymph drainages system becomes overwhelmed.
This is indeed the plugged duct that we always described, except it is not one single duct but hundreds or even thousands of small ducts, and it is not plugged by a single ‘lump’ of milk, but by cells and blood vessels and swelling.
At this point in time, mom has inflammatory mastitis. If managed correctly it should subside and breastfeeding can continue. If not it will complicate and progress, and can have devastating effects on mom’s breastfeeding journey.
The Role of FIL (Feedback Inhibitor of Lactation)
FIL is a protein in breast milk that naturally regulates milk supply. When the breast is full, FIL levels rise and signal the body to slow production. FIL is the the body’s own solution to the problem.
This is why, during mastitis, temporary “breast rest” (not emptying the breast completely) can help reduce oversupply and inflammation. It allows FIL to do its job — restoring balance and easing pressure.
Final Thoughts
The new ABM Protocol #36 empowers mothers and professionals with science-based strategies for managing the mastitis spectrum safely and effectively. Understanding your body helps you find solutions that last — and keeps your breastfeeding journey healthy and positive.
If you’re experiencing pain, fever, or persistent breast issues, please reach out to a lactation consultant or breastfeeding-friendly healthcare provider familiar with this new protocol.
