The Power of the Scent of Breast Milk

In the words of Sarnat et al., ¹ “The sense of smell is the earliest and most fundamental of the special senses to develop in the fetus, as in phylogenetic evolution.” As early as the 28th week of gestation, preterm neonates have the capacity to respond to olfactory stimuli. Fetal ultrasound can demonstrate changes in fetal movements, respiratory patterns, and lingual activity in response to maternal ingestions of foods with strong odors.

Marlier and Schaal ² compared the response of 3–4-day-old term infants to the smelling of human milk as opposed to standard formula and demonstrated that the odor of human breast milk is more attractive to human newborns than standard formula and that this preference is independent of the type postnatal feeding experience. Furthermore, the response to mothers' own breast milk exceeds the response to “stranger” human milk.

Not only is there a powerful immediate response to the scent of milk but also most strikingly is the strength and uniqueness of olfactory memories. Apparently memories of distinctive smells persist and have the potential of recall and association even years later to features and characteristics of the initial stimulus. Delaunay El-Allam et al. ³ documented that early odor memories acquired during breastfeeding can be reactivated and, in turn, influence behavioral processes until at least toddlerhood.

This phenomenon of recall has been coined the “Proustian effect,” a term that refers to the literary description of such a phenomenon by Marcel Proust in his monumental novel “Remembrance of Things Past” ⁴ (or as newly translated “In Search of Lost Time”) wherein Proust describes a character vividly recalling long-forgotten memories from his childhood after smelling a tea-soaked madeleine biscuit.

In the words of Van Campen, ⁵ in his analysis of Proust's oeuvre, “The Proust effect refers to the vivid reliving of events from the past through sensory stimuli. Many of us are familiar with those special moments, when you are taken by surprise by a tiny sensory stimulus (e.g., the scent of your mother's soap) that evokes an intense and emotional memory of an episode from your childhood.” Or as stated by Helen Keller, the renowned blind deaf author: “Smell is a potent wizard that transports you across thousands of miles and all the years you have lived.” ⁶

Given the mentioned, it is not surprising that there has been interest by clinicians in how to capitalize of the power of this basic sensory modality as a clinical tool. As such, this month's issue of Breastfeeding Medicine is of particular interest as it features a study by Tasci and colleague comparing the calming effect of mother's own breast milk odor as opposed to the odor of standard formula. The investigators measured both the clinical pain response and salivary cortisol levels in response to a painful stimulus. What they demonstrated was that not only was there less of a pain response but there was also a lower cortisol response from smelling breast milk. These data strongly support the conclusion that that breast milk has the capacity to mitigate the negative effect of a stressful procedure. These results further suggest that such simple “low tech” essentially no cost noninvasive procedures should be considered as a routine in the care of newborn undergoing painful invasive heel stick blood sampling.

Further studies are clearly needed to delineate more specific details of how to implement this stress preventive practice such as what is the ideal time interval between presenting the scent and the invasive procedures and is there any dose effect. But until such data are generated, clearly one can proceed now using these investigators' methodology and the knowledge of the infants' well-developed sensory modality of smell to utilize breast milk in all beneficent features. It is not just a matter of nutrition, as breast milk can surely be the ultimate comfort food!