A breast infection refers to an inflammatory condition of the breast tissue, which often involves a bacterial invasion. The two most common forms are mastitis, an inflammation that may be infectious, and cellulitis, a bacterial infection of the skin and underlying soft tissue. Symptoms typically include localized pain, redness, swelling, and warmth, sometimes accompanied by systemic signs like fever or flu-like symptoms. The specific cause of a breast infection is highly dependent on an individual’s physiological state, particularly whether they are currently breastfeeding or not.
The Primary Cause: Lactational Mastitis
The most frequent cause of breast infection is lactational mastitis, which occurs in breastfeeding individuals, most commonly within the first few weeks after childbirth. This condition typically arises from a two-step process involving milk stasis and subsequent bacterial proliferation. Milk stasis, or the ineffective removal of milk from the breast, creates an environment where milk components build up and cause localized inflammation.
This milk buildup often results from a blocked milk duct, poor latch by the infant, or infrequent or incomplete emptying of the breast. When milk remains stagnant in the ductal system, it provides a nutrient-rich medium for bacteria already present in the breast. The pressure from the retained milk can also force milk components into the surrounding tissue, triggering an inflammatory reaction.
The bacterial component usually involves common skin flora, most often Staphylococcus aureus, but sometimes Streptococcus species. These microorganisms gain entry into the breast’s ductal system through small cracks or abrasions on the nipple or areola, which are prone to damage from friction or a suboptimal latch. Once inside, the bacteria multiply rapidly in the stagnant milk, leading to an infection characterized by fever, chills, and intense localized pain. Prompt and effective milk removal is considered a primary management strategy because it addresses the underlying issue of stasis and helps flush out infectious agents.
Infections Unrelated to Breastfeeding
Breast infections can also occur in individuals who are not lactating. One common type is periductal mastitis, an inflammation that centers around the milk ducts near the nipple. This condition is often seen in younger, non-lactating individuals and is strongly associated with lifestyle factors.
Periductal mastitis is linked to smoking because chemicals in cigarette smoke are thought to damage the delicate lining of the subareolar ducts. This damage can lead to the ducts becoming blocked and inflamed, creating an environment susceptible to bacterial overgrowth. The infection is generally confined beneath the nipple and may lead to a subareolar abscess.
Duct ectasia involves the widening and shortening of the major milk ducts. While not always infectious, the ducts can fill with thick, stagnant secretions. If these secretions leak into the surrounding tissue, they provoke a severe inflammatory reaction that can introduce a secondary bacterial infection if the duct lining is compromised.
A breast infection may also present as cellulitis, a skin infection that affects the superficial tissue. This type of infection can arise from a break in the skin anywhere on the breast. Cellulitis is generally caused by common bacteria entering through a cut, scratch, or a surgical incision.
Underlying Risk Factors and Contributing Conditions
Chronic health conditions that compromise the immune system’s ability to fight off pathogens are a significant concern. For instance, individuals with diabetes mellitus are at a higher risk of developing infections.
Prior breast surgery, including augmentation, reduction, or mastectomy, increases susceptibility to infection. The presence of foreign materials like breast implants can also complicate infections, as bacteria can form biofilms on the implant surface that are difficult for antibiotics to penetrate.
Factors that directly breach the skin barrier or compromise tissue integrity also elevate risk. Nipple piercings, if not properly maintained, can serve as a persistent portal of entry for bacteria, leading to localized or deeper infections. Conditions that cause immunosuppression, such as chemotherapy, radiation therapy, or certain medications, reduce the body’s ability to control bacterial growth, making an infection more likely to take hold.
Obesity is a recognized contributing factor, as a higher body mass index can be associated with increased moisture and friction under the breast, potentially leading to skin breakdown and cellulitis.