“When a baby suckles at its mother’s breast, a vacuum is created. Within that vacuum, the infant’s saliva is sucked back into the mother’s nipple, where receptors in her mammary gland read its signals. This “baby spit backwash,” as she delightfully describes it, contains information about the baby’s immune status. Everything scientists know about physiology indicates that baby spit backwash is one of the ways that breast milk adjusts its immunological composition. If the mammary gland receptors detect the presence of pathogens, they compel the mother’s body to produce antibodies to fight it, and those antibodies travel through breast milk back into the baby’s body, where they target the infection.”
For the record the technical term for “baby spit backwash” is “retrograde milk flow” (Geddes et al. 2008; Geddes 2009; Geddes et al. 2012; Ramsey et al. 2004).”
Geddes, Donna T., et al. “Tongue movement and intra-oral vacuum in breastfeeding infants.” Early human development 84.7 (2008): 471-477.
Geddes, Donna T., et al. “Tongue movement and intra-oral vacuum of term infants during breastfeeding and feeding from an experimental teat that released milk under vacuum only.” Early human development 88.6 (2012): 443-449.
Ramsay, D. T., Kent, J. C., Owens, R. A., & Hartmann, P. E. (2004). Ultrasound imaging of milk ejection in the breast of lactating women. Pediatrics, 113(2), 361-367.