Mastitis While Breastfeeding: Signs, Causes and What Helps
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In breastfeeding mothers, the NHS says mastitis is usually caused when milk builds up in the breast faster than it is removed. 1 The NHS also says it is important to deal with a blocked duct quickly, because if left it could lead to mastitis. 2 Below is what recognised health bodies say about telling these apart, what they report helps, and when it needs a doctor.
Key takeaways
- The NHS says mastitis in breastfeeding is usually caused when milk builds up faster than it is removed. 1
- The NHS says a blocked duct should be dealt with quickly because, left alone, it could lead to mastitis. 2
- The American Academy of Pediatrics says the best initial treatment for a clogged duct is to keep nursing and drain the breast as much as possible at each feed. 3
- The NHS says to feed frequently and responsively, and to avoid a bra or clothing that is too tight, among ways to lower the risk. 1 1
- The NHS says getting treatment for mastitis as soon as possible can reduce the risk of a breast abscess. 4
**A quick, honest note:** we're not medical professionals - everything here was researched by us from the public sources listed at the bottom of this page, and it isn't professional advice. Read our full note ↓
What is mastitis?
In a breastfeeding mother, the NHS says mastitis is usually caused when milk builds up in the breast faster than it is being removed. In its words: "If you're breastfeeding, mastitis is usually caused when the milk in your breast builds up faster than it's being removed." 1 La Leche League describes how milk moves: it flows through a system of microscopic ducts in the breast that are easily compressed. 5 And the NHS says it is important to deal with a blocked duct quickly, because if left it could lead to mastitis. 2
How can I tell a blocked duct from mastitis?
The NHS says a blocked duct commonly presents as a small, tender lump in the breast. 2 La Leche League says that over an affected area the skin may appear darker, redder or pinker than usual and may feel warm to the touch, and adds that on darker skin redness may not be as easily detected or may not be visible at all. 5 The American Academy of Pediatrics says a clogged duct should be dealt with immediately, because it can lead to a breast infection. 3 Working out which stage you are at is something to check with a professional - this article is only reporting what the sources say.
What causes mastitis when breastfeeding?
The NHS says mastitis is usually caused when milk builds up faster than it is removed, and that long gaps between feeds can create that build-up. 1 1 The American Academy of Pediatrics lists contributors to a clogged duct: an abrupt change in the feeding schedule, inadequate draining of the breast, not varying nursing positions, or wearing clothes or bras that are too tight. 3 The American Academy of Pediatrics also says a clogged duct should be dealt with immediately, because it can lead to a breast infection. 3
What do health bodies say helps?
The American Academy of Pediatrics puts it directly: "The best initial treatment for a clogged duct is to continue nursing, taking care to drain the breast as much as possible with each feeding." 3 The NHS describes gently massaging the lump towards the nipple while the baby feeds. 2
On warmth and cold, the NHS is specific. It describes applying a cloth soaked in warm water, or a warm bath, to encourage the flow - while cautioning not to apply a lot of heat, and not for too long, as this may increase inflammation. 2 Between feeds, the NHS says applying a cold compress may reduce pain. 2 This is general information, not a treatment plan for you personally.
Can a well-fitting bra make a difference?
The NHS lists avoiding a bra or clothing that is too tight and puts pressure on the breasts among the ways to lower mastitis risk. 1 La Leche League puts bra fit conditionally: if you wear a bra, it says, make sure it is well-fitting, supportive and not tight. 5 The American Academy of Pediatrics separately names clothes or bras that are too tight among the contributors to a clogged duct. 3
How can I lower the risk?
The NHS says to feed frequently and responsively, since long gaps between feeds can create a build-up of breast milk. 1 It suggests that, when a mother wants to stop breastfeeding, cutting down feeds gradually is better than suddenly going longer between them. 1 And it lists avoiding a bra or clothing that is too tight among the same set of measures. 1
When does mastitis need a doctor?
The NHS describes the complication plainly: "A breast abscess is a painful build-up of pus in the breast caused by an infection." 4 The NHS says getting treatment for mastitis as soon as possible can help reduce the risk of getting one. 4 It also says you are more likely to have a breast abscess if you have recently had mastitis or have had a breast abscess before. 4
Frequently asked questions
What is mastitis?
In breastfeeding, the NHS says it is usually caused when milk builds up faster than it is removed. 1
How can I tell a blocked duct from mastitis?
The NHS says a blocked duct commonly presents as a small, tender lump; the AAP says a clogged duct should be dealt with immediately because it can lead to infection. 2 3 Which stage you are at is a question for a professional.
Can I keep breastfeeding with mastitis?
The AAP says the best initial treatment for a clogged duct is to keep nursing and drain the breast as much as possible at each feed. 3 Beyond that, this is a question for a professional who knows you.
When does mastitis need a doctor?
The NHS says treating mastitis as soon as possible can reduce the risk of a breast abscess - which it describes as a painful build-up of pus caused by an infection. 4 4
A note from us
We're the team behind Yael & Michal. We are not doctors, nurses, lactation consultants, or psychologists, and nothing here is professional advice.
Everything above was researched by us from public, reputable sources - we name and link every one of them below - and summarized as carefully as we could, as a free resource for other mothers. We do this because we wished something like it had existed for us.
When we name an organisation such as the CDC, the NHS, La Leche League, or the Israeli Ministry of Health, we are only citing their published guidance; it does not mean they endorse, sponsor, approve, or are affiliated with us. They have no involvement with this site, and we never use their logos or seals.
Yael & Michal sells nursing bras, which are comfort garments and not medical devices; we do not claim they prevent, treat, or cure any medical condition. The health information here is written for you as a free resource - it is separate from anything we sell.
We try hard to get it right, and we cite our sources so you can check us. But we are not a medical authority, and this cannot replace talking to a professional who knows you and your baby. Please check anything that matters with your doctor, midwife, or an IBCLC lactation consultant. This content has not been reviewed by a medical professional. Reading this site does not create a doctor-patient relationship, or any other professional relationship, between you and us.
If something feels urgent, contact your healthcare provider or emergency services.
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Sources
- NHS (National Health Service). https://www.nhs.uk/best-start-in-life/baby/feeding-your-baby/breastfeeding/breastfeeding-challenges/mastitis/ (retrieved 2026-07-10).
- NHS. https://www.nhs.uk/baby/breastfeeding-and-bottle-feeding/breastfeeding-problems/breast-pain/ (retrieved 2026-07-10).
- HealthyChildren.org (American Academy of Pediatrics). https://www.healthychildren.org/English/ages-stages/baby/breastfeeding/Pages/Clogged-Milk-Ducts.aspx (retrieved 2026-07-10).
- NHS (National Health Service). https://www.nhs.uk/conditions/breast-abscess/ (retrieved 2026-07-10).
- La Leche League International. https://llli.org/breastfeeding-info/mastitis/ (retrieved 2026-07-10).