Breast milk is a complex biological fluid that is generally considered the optimal source of nutrition and immune support for an infant. The risk of pathogen transmission depends greatly on the specific infectious agent, the mother’s overall health, and her treatment status. For the vast majority of common maternal infections, the benefits of continued breastfeeding, which include providing the infant with protective antibodies, far outweigh the minimal risk of transmitting the illness.
Understanding How Pathogens Enter Breast Milk
Pathogens, such as viruses and bacteria, can enter breast milk through several biological routes. The most common pathway involves the transfer of agents from the mother’s bloodstream into the milk-producing tissue of the mammary gland. This process is similar to how immune cells move from the blood into the milk ducts.
Once in the breast tissue, infectious agents can be found freely suspended in the milk serum or contained within maternal immune cells that naturally migrate into the milk. Viruses like Human Immunodeficiency Virus (HIV) utilize both mechanisms for potential transfer. Pathogens can also enter the milk directly from an infection in the breast tissue itself, such as in cases of mastitis or local viral lesions.
Infections That Require Breastfeeding Modification
For a small number of serious infections, the risk of transmission through breast milk is significant enough to warrant modification or, in some cases, complete cessation of breastfeeding. One of the most recognized examples is Human Immunodeficiency Virus (HIV), which can be transmitted to the infant via breast milk. The risk of transmission is substantially reduced, to less than one percent, when the mother maintains an undetectable viral load through consistent use of antiretroviral therapy (ART) during pregnancy and while breastfeeding.
In resource-rich settings, healthcare providers often recommend that mothers living with HIV avoid breastfeeding entirely to eliminate transmission risk. However, in other regions, the World Health Organization may recommend breastfeeding alongside ART, balancing the transmission risk against the high risk of infant mortality from malnutrition and other infections if formula is not available or safe. The Human T-lymphotropic Virus Type I and II (HTLV-I/II) are also retroviruses where transmission primarily occurs through breastfeeding, and avoidance of breastfeeding is typically recommended to prevent infection.
Active, untreated tuberculosis (TB) is another serious concern, though the primary risk to the infant is airborne exposure, not the milk itself. For mothers with active TB, temporary separation from the infant is often recommended, and the infant can be fed expressed breast milk, provided there are no open lesions on the breast tissue. Decisions regarding these high-risk infections must always be made in close consultation with a healthcare provider, who can weigh the mother’s treatment status and local public health guidelines.
Common Illnesses Where Breastfeeding Can Continue
For the vast majority of common maternal infections, continued breastfeeding is not only safe but highly recommended. Illnesses such as the common cold, influenza, most instances of COVID-19, and mild gastroenteritis typically do not require any modification to the feeding plan. In these scenarios, the mother’s body begins producing targeted antibodies immediately upon exposure to the pathogen.
These antibodies, specifically secretory IgA (sIgA), are transferred directly to the infant through the breast milk. The sIgA antibodies line the infant’s digestive and respiratory tracts, neutralizing the pathogen before it can cause a serious infection. This mechanism provides the infant with passive immunity, protecting them against the very illness the mother is experiencing. Furthermore, the mother’s milk also contains white blood cells and other immune factors that help support the infant’s still-developing immune system.
Even in cases of mastitis, which is an infection of the breast tissue, breastfeeding is generally encouraged and can even help clear the infection. The bacteria causing mastitis is typically part of the normal skin flora and does not pose a significant risk to the healthy, full-term infant.