Although the idea may be surprising to many, new research from a team in Japan indicates that smelling the breastmilk of the mother can help calm a newborn baby, even reducing the infant’s physical experience of pain.

The researchers compared the effect of different types of milk smells on the distress exhibited by 48 infants during a routine heel stick (a procedure used to get a small blood sample).  Distress was measured by the infant’s crying, grimacing, and motor activities as well as by the concentration of salivary cortisol, a hormone present in saliva during times of stress or pain.  Infants were assigned to one of the following groups of odors: their own mother’s breastmilk, another mother’s breastmilk, a milk-based formula, or the control (no milk odor present).

Both behavioral and chemical measurements of distress were lower among infants who were able to smell their own mother’s milk; they cried and made physical signs of pain less frequently than the infants in other categories, and they had less concentrated levels of cortisol in their saliva than their non-maternal breastmilk counterparts.

Not only did infants react with less behavioral and chemical indications of pain if they could smell their own mother’s breastmilk, but there was also no indication that the smell of another mother’s breastmilk or the odor of formula made any significant difference over the smell of nothing at all.

Although researchers have previously demonstrated the soothing effect the smell of a mother’s breastmilk can have on her child during painful procedures, there was little to suggest that the infant’s own mother’s milk would have more of a calming effect than that of another mother or of formula—until this study.

Will Maternal Breastmilk Become an Analgesic for Newborns?
Because there was no significant change in the reaction of the newborns to the heel stick between the control group and the non-maternal milk or formula groups, there may be a particular component to a mother’s milk that her baby recognizes and responds to.  If smelling the milk relieves pain and calms the infant, it is reasonable to assume that this research may have clinical applications.

It is possible that this calming effect comes from the infant’s recognition of the individual smell of the breastmilk, as the infants involved in the study were only breastfed babies.  The researchers suggest, however, that the infants may be calmed by the presence of certain (major histocompatibility complex) genes in the milk that are familiar and comforting to them, and that another mother’s milk with similar genes may have a similar calming effect.

Because it is unclear as to why the maternal breastmilk reduces distress in newborns, there are few immediate direct clinical implications of this research; additional research on the topic may clarify whether maternal breastmilk is more calming than amniotic fluid or other familiar smells, for instance, and whether the same calming effect can be demonstrated in formula-fed infants or infants at different ages (the study participants were five days old).

Regardless of whether maternal breastmilk odor becomes a commonplace analgesic for newborns, the calming properties of a mother’s milk only serve to bolster the reputation that breastfeeding has earned for its ability to bond mother and baby and protect infant health.