Mastitis is an inflammation of the breast tissue that can range from a mild, localised tenderness to a severely painful, flu-like illness that leaves you unable to function normally. It is one of the most common breast conditions managed by our practice, and the good news is that with prompt and appropriate treatment, the vast majority of cases resolve completely and quickly.

Most people associate mastitis with breastfeeding — and it is indeed most common in new mothers — but breast infection can and does affect women who are not breastfeeding, as well as, rarely, men. Understanding the different types of breast infection, when to seek specialist care, and how to distinguish mastitis from more serious conditions are all important parts of managing this common problem well.

What Is Mastitis?

Mastitis is an inflammation of the breast tissue. It may occur with or without a bacterial infection, and it may or may not progress to abscess formation — a localised collection of pus within the breast. The term "mastitis" is often used interchangeably with "breast infection," though strictly speaking, inflammation can occur without active bacterial infection, particularly in the early stages.

The hallmark symptoms are localised breast pain, redness, warmth, and swelling — often in a wedge-shaped area of the breast — combined with systemic symptoms including fever, chills, and flu-like lethargy when infection is established. The breast typically feels hard and tender in the affected area and the skin may appear flushed and feel hot to touch.

Types of Mastitis and Breast Infection

Not all breast infections are the same. Understanding the type is important, as it determines the most appropriate treatment approach and the likelihood of recurrence.

Lactational Mastitis

Lactational mastitis is the most common type, affecting an estimated 1 in 5 breastfeeding women, most commonly within the first three months after birth — though it can occur at any point during breastfeeding.

It develops when milk becomes stagnant in one or more ducts — a process known as milk stasis — providing a warm, nutrient-rich environment in which bacteria can proliferate. The most common causative organism is Staphylococcus aureus, though other bacteria including Streptococcus and, increasingly, Staphylococcus epidermidis are also implicated. Bacteria typically enter the breast through small cracks or fissures in the nipple caused by poor latch or frequent feeding.

Factors that contribute to milk stasis and therefore lactational mastitis include infrequent or missed feeds, poor attachment or latch, rapid weaning, pressure on the breast from tight clothing or a poorly fitted bra, and maternal fatigue and stress. A cracked or sore nipple that has been difficult to manage is also a common preceding feature.

Non-Lactational (Periductal) Mastitis

Non-lactational mastitis — also called periductal mastitis or subareolar abscess — affects women who are not breastfeeding, most commonly in their 30s and 40s. It arises from inflammation and infection of the ducts beneath the nipple-areola complex and is strongly associated with cigarette smoking, which damages the ductal epithelium and predisposes to bacterial colonisation.

Periductal mastitis typically presents as a painful, tender, red swelling beneath or adjacent to the nipple. It can be recurrent and may progress to abscess formation, nipple inversion (as the inflamed and scarred ducts contract), or — if inadequately treated — a mammary duct fistula (an abnormal connection between an infected duct and the skin surface that causes persistent discharge).

Because periductal mastitis involves chronic ductal inflammation that can be difficult to fully eradicate, recurrence is common, and some women require surgical intervention — excision of the affected ducts — to achieve lasting resolution.

Idiopathic Granulomatous Mastitis

Idiopathic granulomatous mastitis (IGM) is a rare but increasingly recognised inflammatory condition of the breast that can closely mimic both breast abscess and, on imaging, breast cancer. It presents most commonly in young to middle-aged women, often within a few years of pregnancy, and causes tender, sometimes fluctuant masses that may drain spontaneously and form persistent skin sinuses.

The cause is not fully understood, though immune-mediated mechanisms are thought to be involved. IGM can be difficult to treat — it may not respond fully to antibiotics, tends to recur, and often requires a prolonged course of management including corticosteroids or steroid injection into the breast but rare cases, surgery. A tissue biopsy is essential to establish the diagnosis and exclude malignancy before treatment is commenced.

If you have been told you have a recurring or complex breast infection that has not responded to standard treatment, specialist review is strongly recommended.

Symptoms of Breast Infection and Mastitis

While symptoms vary between types and severity, common features include:

• Localised breast pain, often described as aching, burning, or throbbing
• Redness and warmth over the affected area of the breast
• Swelling and firmness or a palpable lump in the affected area
• Fever — typically above 38°C — and flu-like symptoms including chills, body aches, and fatigue
• Nipple discharge, which may be white, yellow, or blood-tinged
• Swelling or tenderness extending to the armpit in more severe cases

In non-lactational mastitis, systemic symptoms may be less prominent, and the presentation may be more of a chronic, smouldering inflammation with a tender, indurated area beneath the nipple that comes and goes over weeks or months.

Mastitis vs. Breast Abscess — What Is the Difference?

Mastitis refers to the inflammation and infection of breast tissue. A breast abscess is a localised collection of pus that forms when the infection is not controlled — essentially, an infected cavity within the breast tissue.

An abscess tends to present as a more defined, fluctuant (fluid-filled and compressible) lump within an area of surrounding redness and tenderness. Systemic symptoms such as fever are often more pronounced. While mastitis can usually be managed with antibiotics alone, a breast abscess generally requires drainage in addition to antibiotics — the pus cannot be sterilised by antibiotics alone and must be physically removed to allow healing.

Distinguishing between mastitis and abscess is best done with an ultrasound, which can identify whether a fluid collection has formed, how large it is, and whether drainage is likely to be required.

How Is Mastitis Diagnosed?

For most straightforward cases in breastfeeding women, the diagnosis is clinical — based on the characteristic symptoms and examination findings. However, imaging and further investigation are warranted in several situations.

Ultrasound is the most useful imaging modality for breast infection. It confirms the diagnosis, characterises the extent of the inflammation, identifies whether an abscess has formed, and guides drainage if needed. It is painless, involves no radiation, and can be performed quickly.

Mammography may be recommended in women over 40 where malignancy needs to be excluded alongside infection, or where the presentation is atypical.

Breast milk culture — a sample of breast milk can be sent for microbiological analysis to identify the causative organism and guide antibiotic selection, particularly in recurrent or treatment-resistant cases.

Tissue biopsy is strongly recommended when mastitis does not respond to antibiotics as expected, when imaging shows features that are atypical for simple infection, or when there is clinical concern about an underlying malignancy. This is particularly important given that inflammatory breast cancer — a rare but aggressive form of breast cancer — can closely mimic the appearance of mastitis (see below).

The Critical Importance of Excluding Inflammatory Breast Cancer

This is a point that deserves specific attention. Inflammatory breast cancer (IBC) is a rare but aggressive form of breast cancer in which cancer cells block the lymphatic vessels in the skin of the breast, producing redness, warmth, swelling, and skin thickening that can be virtually indistinguishable from mastitis or cellulitis on first presentation.

Unlike most breast cancers, IBC frequently does not present with a distinct lump, which means it can be — and often is — initially attributed to infection and treated with antibiotics. If the skin changes do not improve promptly and substantially with a course of antibiotics, this must be taken seriously and specialist review sought without further delay.

Any breast redness and swelling that:

• Does not improve clearly within 5–7 days of commencing appropriate antibiotics
• Is not associated with fever or a clearly infective picture
• Occurs in a woman who is not breastfeeding, without an obvious precipitating cause
• Is accompanied by skin thickening or a peau d'orange (orange peel) texture
• Involves rapid swelling of the entire breast rather than a localised area

...warrants urgent specialist assessment and imaging to exclude inflammatory breast cancer before continuing to treat presumptively as infection.

At Breast & Surgical Oncology at The Poche Centre, we are vigilant about this distinction and assess any atypical or treatment-resistant breast infection with this in mind.

Treatment of Mastitis

Lactational Mastitis

Continue breastfeeding or expressing. This is the single most important piece of advice for women with lactational mastitis. Stopping feeds suddenly worsens engorgement and milk stasis, which prolongs the condition. Frequent feeding or expressing from the affected breast — starting on the affected side if possible, as the let-down reflex is often stronger at the beginning of a feed — is essential to clear the stasis driving the infection. Breastfeeding during mastitis is safe for the baby.

Antibiotics. A course of antibiotics effective against Staphylococcus aureus — typically dicloxacillin or cefalexin for 10–14 days — is prescribed when infection is established. It is important to complete the full course even if symptoms begin to improve quickly, as under-treatment increases the risk of abscess formation and recurrence.

Analgesia and anti-inflammatories. Ibuprofen (where not contraindicated) is particularly helpful as it addresses both pain and the inflammatory component of mastitis. Paracetamol can be used in addition. Both are safe during breastfeeding.

Warmth before feeding, cold after. Gentle warmth applied to the breast before a feed helps encourage milk flow and let-down. Cold compresses between feeds help reduce inflammation and provide pain relief.

Rest and hydration. Mastitis takes a real toll on the body, particularly when accompanied by fever. Rest and adequate fluid intake support recovery.

Lactation consultation. If mastitis is recurrent or if latch problems are suspected as a contributing factor, referral to a lactation consultant is strongly recommended. Addressing the underlying feeding mechanics can significantly reduce the risk of further episodes.

Non-Lactational (Periductal) Mastitis

Antibiotics are the first-line treatment, though the choice may differ from lactational mastitis as the bacterial spectrum is often broader. Smoking cessation is strongly advised and genuinely reduces recurrence risk. For recurrent episodes that do not resolve with antibiotics, or where a fistula has formed, surgical excision of the affected ducts (total duct excision) may be recommended to achieve lasting resolution.

Breast Abscess Drainage

When a breast abscess has formed, drainage is required. The preferred approach at our practice is ultrasound-guided needle aspiration — a minimally invasive outpatient procedure performed under local anaesthetic in which a needle is inserted into the abscess cavity under real-time ultrasound guidance to aspirate the pus. This is effective for most abscesses and avoids the need for a formal surgical incision and drainage. Repeat aspiration may be needed for larger or recurrent collections.

For abscesses that are very large, multiloculated (multiple compartments), or have not responded to repeated needle aspiration, surgical incision and drainage under general or local anaesthetic may be required. A small incision is made over the most fluctuant point, the pus is drained, and the cavity is irrigated and dressed. This heals from the inside out over a period of days to weeks, with regular dressing changes.

When to Seek Specialist Review for Mastitis

Most cases of lactational mastitis can be managed by your GP or midwife without specialist input. However, you should seek specialist breast assessment if:

• Symptoms are not clearly improving within 48–72 hours of commencing antibiotics
• An abscess has formed or is suspected — prompt drainage prevents it from enlarging
• Mastitis has recurred two or more times
• You are not breastfeeding and have developed a breast infection
• A lump persists after the acute infection has resolved — this requires further assessment to ensure there is no underlying pathology
• Redness and swelling of the breast are not responding to antibiotics as expected and inflammatory breast cancer needs to be excluded
• Nipple inversion has developed alongside recurrent infection
• A skin opening or sinus tract has formed near the areola

Breast Infection and Mastitis Assessment in North Sydney

Our team at Breast & Surgical Oncology at The Poche Centre regularly assesses and manages breast infections at all levels of complexity — from straightforward lactational mastitis requiring antibiotic management, to recurrent periductal mastitis requiring surgical duct excision, to complex cases requiring careful exclusion of underlying malignancy.

We offer prompt appointments, ultrasound-guided abscess drainage in appropriate cases, and the reassurance of specialist expertise when your breast infection is not following the expected course.