Mastitis
Mastitis is inflammation of the breast, most familiar as a complication of breastfeeding but also occurring outside it. It typically produces a painful, red, swollen area of breast along with fever and a flu-like feeling of illness, often coming on rapidly over hours. The understanding of why it happens has shifted in recent years: it is now recognised as primarily an inflammatory process driven by milk accumulation and tissue swelling rather than an infection in every case, and this has changed the advice given. Most episodes settle with effective milk removal, anti-inflammatory medication, and rest, with antibiotics reserved for cases that do not improve or where infection is clearly present.
What is it?
Mastitis means inflammation of the breast. The term covers a spectrum rather than a single condition, and understanding where a given episode sits on that spectrum determines how it should be treated.
During breastfeeding, the sequence usually begins with milk accumulating in part of the breast. This happens when milk is not effectively removed—because of a missed or shortened feed, poor attachment, a sudden change in feeding pattern, pressure from a tight bra or sleeping position, or oversupply. Milk builds up in a segment, the tissue around it swells, and that swelling compresses the surrounding ducts, making drainage harder still. This self-reinforcing cycle is the core of the problem.
The understanding of what follows has changed meaningfully in recent years, and this has altered the advice given.
Mastitis was traditionally conceived as an infection, with antibiotics as the automatic response. Current thinking frames it primarily as an inflammatory condition. Milk accumulation causes tissue swelling and inflammation, which produces the pain, redness, and fever. Bacteria are frequently present but are not always the driving problem, and many episodes resolve with effective milk removal and anti-inflammatory treatment alone. Infection does supervene in a proportion of cases, particularly where there is a cracked nipple providing an entry point, and these cases need antibiotics.
This reframing has two practical consequences. It explains why anti-inflammatory medication is more useful than previously appreciated, and it explains why a period of observation with effective milk removal, rather than immediate antibiotics, is now reasonable in milder cases.
There is also growing interest in the role of the breast’s own microbial community, with the suggestion that disruption of the normal balance of bacteria within the milk ducts contributes. This remains an area of active research, and claims about specific probiotic treatments have run ahead of the evidence.
Several factors increase risk. Damaged or cracked nipples, usually from poor attachment, provide an entry point for bacteria and are among the strongest predictors. Infrequent or missed feeds, abrupt changes in feeding pattern, and anything that interrupts routine removal all contribute. Oversupply produces more milk than is being removed. Pressure on the breast from tight clothing, an ill-fitting bra, a seatbelt, or sleeping position can obstruct a segment. Previous mastitis raises the risk of another episode. Maternal fatigue, stress, and illness are associated. Nipple shields and pumping, where not well managed, can contribute.
A distinct point worth making is that aggressive deep massage of the breast, long recommended for blocked ducts and mastitis, is now discouraged. It appears to worsen tissue swelling and can cause further damage. Gentle handling, lymphatic drainage techniques directed toward the armpit, and cold application are preferred to vigorous massage of the affected area.
Non-lactational mastitis occurs outside breastfeeding and takes several forms.
Periductal mastitis affects the ducts beneath the nipple and is strongly associated with smoking. It produces pain, redness, and swelling in the area around the nipple, tends to recur, and can progress to abscess and to a persistent discharging track known as a mammary duct fistula. Stopping smoking is the most effective intervention and, without it, recurrence is likely.
Granulomatous mastitis is an uncommon inflammatory condition producing firm, often painful masses that can ulcerate and that closely mimic breast cancer. It occurs most often in women within a few years of pregnancy, requires biopsy to diagnose, and is managed quite differently from infective mastitis.
Infection of a skin cyst or hair follicle, and inflammation after trauma or surgery, also produce localised breast inflammation.
The symptoms of lactational mastitis are distinctive, and their rapid onset is characteristic.
A painful area of breast develops, typically firm, red, warm, and tender. It usually affects one segment rather than the whole breast, often producing a wedge-shaped red area.
Fever with chills, shivering, and aching develops in many women and can be sudden and striking. Women frequently describe feeling as though they have influenza, and the systemic illness can be out of proportion to how the breast looks. A woman who suddenly feels dreadful while breastfeeding should check her breasts, since the general illness sometimes precedes noticeable local symptoms.
Feeding on the affected side is painful, and milk flow from that breast may be reduced temporarily.
The speed of onset distinguishes mastitis from most other breast conditions. Symptoms typically develop over hours.
One caution requires emphasis, and it applies throughout breast medicine. Inflammatory breast cancer produces redness, swelling, warmth, and skin thickening that can look very similar. The distinguishing features are that it develops over weeks rather than hours, usually occurs without fever, and crucially does not improve with antibiotics. Any breast inflammation that has not clearly responded to appropriate treatment requires specialist assessment and biopsy rather than a further antibiotic course. This applies to breastfeeding women as well—pregnancy-associated and lactation-associated breast cancer exists and is frequently diagnosed late precisely because symptoms are attributed to normal or infective changes.
Diagnosis is clinical in the typical case.
The combination of a tender, red, swollen segment of breast with fever in a breastfeeding woman is characteristic, and no investigation is needed where the episode responds to treatment as expected.
Ultrasound becomes important where symptoms persist. Its role is to distinguish simple inflammation, which requires continued milk removal and antibiotics, from an abscess, which requires drainage. It is indicated where there has been no improvement after 48 hours of appropriate antibiotics, where a discrete fluctuant lump is present, and where the clinical picture is atypical.
Milk culture is not routinely performed but is useful where infection is severe, recurrent, acquired in hospital, or failing to respond, since it identifies the organism and its sensitivities.
Mammography and biopsy are reserved for inflammation that does not resolve. In any woman whose breast inflammation persists despite adequate treatment, biopsy of the affected area is appropriate, and this remains true during breastfeeding.
Assessment of feeding is as important as assessment of the breast. Observing a feed, checking attachment, and reviewing the feeding pattern identifies the cause in many cases, and addressing it prevents recurrence. This is where an infant feeding specialist or lactation consultant adds more value than any medication.
Important to Know
The single most important message is that breastfeeding should continue from the affected breast. Milk removal is the treatment, and stopping makes the situation worse by allowing further accumulation. Care is provided by primary care clinicians, midwives, health visitors, and infant feeding specialists, with breast services involved where an abscess or atypical presentation is suspected.
This bears emphasis because the instinct runs the other way. A woman with a painful, red, infected-feeling breast reasonably assumes she should rest it and that the milk may be unsafe. Neither is true. The milk is safe for the baby, including where antibiotics are being taken, since the antibiotics used in this situation are compatible with breastfeeding. Feeding frequently from the affected side is the most effective thing she can do.
Where feeding directly is too painful, expressing from that breast achieves the same purpose and should continue until direct feeding is comfortable again. Feeding from the unaffected side alone is not sufficient.
The practical measures that help are worth knowing in detail, since they are what resolve most episodes.
Feed frequently and on demand, starting on the affected side when the baby’s suck is strongest, and ensuring the breast feels softer afterwards. Vary feeding positions to help drain different parts of the breast.
Apply warmth briefly before a feed to encourage let-down, and cold afterwards to reduce swelling and pain. Cold is more useful than many women expect, since reducing tissue swelling addresses the underlying mechanism.
Take ibuprofen regularly unless contraindicated. Its anti-inflammatory effect addresses the swelling that drives the problem, and it is compatible with breastfeeding. Paracetamol can be added for pain.
Rest, drink adequately, and get help with other responsibilities. Fatigue is both a risk factor and a consequence.
Avoid vigorous deep massage of the inflamed area, which current guidance now advises against because it worsens swelling. Gentle stroking toward the armpit, which assists lymphatic drainage, is preferred.
Check for the cause. A cracked nipple, poor attachment, a missed feed, a tight bra, or a change in routine is usually identifiable, and correcting it prevents the next episode. Observation of a feed by someone skilled is often more valuable than any prescription.
On antibiotics, the approach has become more selective. They are given where a woman is systemically unwell at the outset, where there is an infected nipple fissure, where symptoms are severe, or where there is no improvement after 12 to 24 hours of effective milk removal and anti-inflammatory treatment. Many milder episodes settle without them. Where antibiotics are given, the full course should be completed, and improvement should be apparent within 48 hours.
Failure to improve within 48 hours of antibiotics is the trigger for ultrasound. By that point, either an abscess has formed and needs draining, the organism is resistant and a different antibiotic is required, or the diagnosis is wrong. Continuing to wait is the most common path to an abscess that could have been identified earlier.
Recurrent mastitis warrants a thorough review rather than repeated courses of antibiotics. The usual cause is an unaddressed feeding problem—attachment, positioning, oversupply, or a pattern of long gaps—and resolving it prevents further episodes. Persistent nipple damage should be treated. Where recurrence continues despite this, milk culture and specialist assessment are appropriate.
For non-lactational mastitis, the approach differs. Periductal mastitis in a smoker requires smoking cessation as the primary intervention, since recurrence is otherwise likely whatever antibiotics are given. Granulomatous mastitis requires biopsy and specialist management rather than repeated antibiotic courses.
A word about stopping breastfeeding is appropriate. Mastitis is a common reason women wean earlier than they intended, often believing they have no alternative. In almost all cases, continuing is both possible and beneficial, and support makes the difference. Where a woman does decide to stop, this should be done gradually rather than abruptly, since sudden cessation during mastitis risks worsening the engorgement and provoking an abscess.
The caution about non-resolving inflammation deserves a final statement. Any breast inflammation that has not clearly improved with appropriate treatment requires specialist assessment and biopsy, not another antibiotic prescription. This applies during breastfeeding as much as outside it. Inflammatory breast cancer and lactation-associated breast cancer are both diagnosed late with some regularity, and the mechanism is almost always repeated empirical treatment of what was assumed to be infection.
Care is provided by primary care, midwifery, health visiting, and infant feeding services, with breast services and radiology involved where symptoms persist. Clinical findings and the response to treatment are what guide management, with imaging reserved for cases that do not follow the expected course.
Patient education plays an important role. Understanding that milk removal is the treatment, that breastfeeding should continue, that anti-inflammatory medication is genuinely useful, that not every episode needs antibiotics, that aggressive massage is no longer advised, and that failure to improve within 48 hours needs reassessment all contribute to appropriate care and to breastfeeding continuing where a woman wishes it to.
Red flag symptoms include failure to improve within 48 hours of starting antibiotics; a distinct firm or fluctuant lump developing within the inflamed area, suggesting abscess; high fever with rigors, confusion, a racing heart, or low blood pressure, suggesting severe infection requiring urgent care; rapidly spreading redness; skin that is becoming dusky, blistered, or breaking down; breast inflammation that has not responded to appropriate treatment, which requires assessment to exclude inflammatory breast cancer; a persistent lump remaining after the inflammation has settled; inflammation in a woman who is not breastfeeding; and recurrent episodes in the same area. These warrant prompt medical evaluation.