The straightforward answer to whether breastfed babies get sick is yes, they do. However, infants who receive human milk generally experience illnesses with less frequency and reduced severity compared to those who are formula-fed. Breast milk acts as a dynamic biological defense system, providing protection against a wide range of common pathogens. This protective effect results from complex, bioactive components transferred from mother to baby, supporting the infant’s developing immune system.
How Breast Milk Builds Immunity
Breast milk delivers passive immunity through biological ingredients suited to the infant’s immature digestive and immune systems. One primary immune factor is secretory Immunoglobulin A (sIgA), an antibody that coats the lining of the baby’s respiratory and intestinal tracts. sIgA binds to bacteria and viruses, preventing them from attaching to mucosal surfaces and causing infection, without being absorbed into the baby’s bloodstream.
Human milk also contains living immune cells, such as macrophages and lymphocytes, which are part of the mother’s immune defenses. Macrophages engulf and destroy harmful microbes, while lymphocytes are specialized white blood cells that attack pathogens or coordinate the immune response. This transfer helps the infant fight off infections encountered in their shared environment.
Another component is lactoferrin, a protein that plays a dual role by binding to iron in the gut, limiting the iron supply necessary for harmful bacteria growth. Lactoferrin also possesses direct antimicrobial and anti-inflammatory properties. Human Milk Oligosaccharides (HMOs) are complex sugars that act as a prebiotic, feeding beneficial bacteria in the infant’s gut and promoting a healthy microbiome that crowds out pathogenic organisms.
HMOs also function directly as “decoys,” mimicking the binding sites on the infant’s cell surfaces where pathogens would normally attach. By binding to the HMOs instead, the harmful microbes are neutralized and safely passed out of the body. The combination of these factors—antibodies, live cells, antimicrobial proteins, and prebiotics—creates a robust, multi-layered shield that protects the baby from infection.
Illnesses Where Breastfeeding Offers Protection
The immunological properties of breast milk translate into reduced rates and severity of infectious diseases during infancy. Protection is strong against gastrointestinal infections, which cause diarrhea and vomiting, resulting in a much lower incidence among breastfed infants. This defense is largely due to sIgA and lactoferrin acting directly on the gut lining, the primary entry point for enteric pathogens.
Breastfeeding also offers protection against acute respiratory infections, including pneumonia and respiratory syncytial virus (RSV). Infants exclusively breastfed for at least four months have a lower risk of hospitalization for lower respiratory tract infections. Continuous exposure to maternal antibodies helps neutralize airborne viruses and bacteria.
Ear infections, or acute otitis media, are less common in breastfed babies. Studies indicate that as little as three months of breastfeeding can lower the risk of ear infections in the first year of life. Breastfeeding is also correlated with a reduced risk of Sudden Infant Death Syndrome (SIDS). Beyond acute illnesses, the early immunological programming provided by human milk is associated with a reduced risk of developing chronic conditions later in childhood, such as asthma and allergies. This protective effect is related to how breast milk components, like HMOs, help regulate and mature the infant’s immune system, promoting tolerance rather than hypersensitivity.
Protection After Weaning
The immediate, passive immunity provided by the antibodies and living cells in breast milk ceases shortly after weaning. Once the continuous supply of these protective factors stops, the direct defense against common acute infections like colds, flu, and ear infections gradually diminishes. The infant’s own immune system must then take over the full responsibility of pathogen defense.
However, the advantages of early exposure to human milk extend beyond active nursing, contributing to long-term health benefits. Breast milk is thought to “program” the infant’s immune system and gut microbiome, creating a foundation for a mature and balanced immune response. This programming effect is associated with a sustained, reduced risk for chronic conditions that manifest later in life. Specific long-term benefits include a lower incidence of conditions such as Type 1 diabetes and childhood leukemia. This enduring protection highlights that the impact of breast milk establishes a more resilient and regulated internal system.