Mastitis symptoms and treatment: When nursing moms need care

Mastitis is one of the more common complications of breastfeeding — estimates suggest it affects between 3% and 20% of nursing mothers, most often in the first few weeks postpartum. It can feel alarming when it arrives: one hour you feel fine, and hours later you have flu-like symptoms and a painful, hot patch on your breast. Understanding what mastitis is, how it differs from a clogged duct, and when you need medical treatment helps you respond quickly and avoid complications.

What causes mastitis?

Mastitis is inflammation of breast tissue, most commonly caused by a blocked milk duct that becomes colonized with bacteria. When milk is not fully drained from a duct — due to infrequent feedings, a poor latch, engorgement, or pressure from a tight bra — it creates an environment where bacteria can grow. Staphylococcus aureus is the most common culprit, though other organisms can be responsible.

The first sign of trouble is often a clogged duct: a tender, palpable lump without systemic symptoms. If milk stasis continues, bacteria proliferate and the blocked duct progresses to a full infection — mastitis.

Clogged duct vs. mastitis: how to tell the difference

The practical distinction that guides treatment is whether you have systemic symptoms — particularly fever:

• Clogged duct: A tender lump or firm area in the breast. Skin color looks normal or very mildly pink. No fever. No flu-like symptoms. The area may feel warm but the discomfort is localized.
• Mastitis: A warm, reddened, swollen area of the breast — often in a wedge pattern following a duct. Accompanied by fever above 100.4°F (38°C), chills, body aches, and fatigue. The systemic symptoms often precede or accompany the breast symptoms and can feel like the flu.

The treatment changes with this distinction. A clogged duct can often be resolved at home with frequent nursing, warm compresses, gentle massage, and positioning that helps fully drain the affected area. Mastitis requires antibiotics.

Symptoms of mastitis

Classic mastitis presents with a combination of local and systemic findings:

• A hot, reddened, firm, painful area of one breast — typically wedge-shaped
• Swelling or engorgement in the affected area
• Fever above 100.4°F (38°C) — often 101°F or higher
• Chills and body aches
• Fatigue, sometimes severe
• Headache

Onset is typically rapid — within hours. Many women describe feeling perfectly fine, then suddenly feeling as if they have the flu, shortly followed by recognizing the breast symptoms. The speed of onset is one of the hallmarks of mastitis.

Treatment: antibiotics and continued feeding

Mastitis is a bacterial infection and requires antibiotics to clear. The standard first-line treatment is a 10–14 day course of dicloxacillin or cephalexin, both of which cover Staphylococcus aureus effectively. For women with penicillin allergy, clindamycin is an alternative. Both are considered safe for the nursing infant.

Equally important: do not stop breastfeeding or pumping. Continuing to empty the breast prevents milk stasis — the very condition that allows bacteria to thrive. Milk from a breast with mastitis is safe for the baby. Stopping nursing during mastitis increases the risk of worsening infection and abscess formation.

Supportive care alongside antibiotics includes:

• Warm compresses before feedings to encourage milk flow
• Cold compresses after feedings to reduce inflammation and discomfort
• Ibuprofen or acetaminophen for pain and fever (both are safe during breastfeeding)
• Rest — as much as possible with a newborn
• Staying hydrated

Most women begin to feel significantly better within 24–48 hours of starting antibiotics. If you're not improving after 48–72 hours on antibiotics, contact your provider — this may indicate a resistant organism, an abscess, or another cause.

The risk of abscess: why prompt treatment matters

If mastitis is not treated promptly, or if treatment is inadequate, the infection can progress to a breast abscess — a localized collection of pus that cannot be cleared with antibiotics alone. An abscess feels like a fluctuant (soft, fluid-filled), very tender lump, and typically does not respond to antibiotics. Treatment requires needle aspiration or surgical incision and drainage.

Abscess formation can occur within 24–48 hours in inadequately treated mastitis. This is why starting antibiotics early — at the first sign of fever and breast redness — is important rather than waiting to see if symptoms resolve on their own.

When to visit urgent care

Severe mastitis with high fever may lead to dehydration—see our guide on when urgent care can provide IV fluids.

Urgent care is a practical and appropriate option for nursing mothers who develop mastitis symptoms, particularly when it's difficult to get a same-day appointment with an OB or primary care provider. An urgent care provider can diagnose mastitis based on your symptoms and physical exam and prescribe the antibiotics you need. Bring your baby's pediatrician's contact information if possible, and mention any antibiotic allergies. If a very tender, fluctuant lump is present that doesn't improve with antibiotics, or if you develop worsening redness extending from the original site, seek evaluation for possible abscess or a more serious skin infection — an urgent care provider can assess whether referral for ultrasound or drainage is needed.