For a newborn, locating and latching onto the mother's breast is the foundational social interaction. This pivotal moment not only influences the newborn's survival but also determines the mother's physiological (lactation) and psychological (attachment) engagement, as well as the long-term health of both the child and the mother. However, according to the WHO, three out of five newborns are not exclusively breastfed for the recommended 6 months, and several recent studies point to suboptimal rates of breastfeeding initiation in the maternity ward, partly due to difficulties with oral latching, insufficient sucking, or refusal of the breast. This situation compromises the initial intake of colostrum/milk, as well as the establishment of early emotional bonds. A wealth of research data from biology, psychology, and pediatrics shows that neonatal and maternal sensory experiences play a central role in the initiation of breastfeeding. However, our understanding of the sensory and behavioral mechanisms at play remains unclear. While visual and auditory interactions have been extensively documented, other sensory modalities-touch, chemoreception, and kinesthesia-remain largely overlooked, even though their critical role has been documented in other mammals. The inves will focus on the role of olfaction in organizing the adaptive responses of the newborn to the mother's breast and of the mother to her baby.

A wealth of research data from biology, psychology, and pediatrics shows that neonatal and maternal sensory experiences play a central role in the initiation of breastfeeding. However, our understanding of the sensory and behavioral mechanisms involved remains unclear. While visual and auditory interactions have been extensively documented, other sensory modalities-touch, chemoreception, and kinesthesia-have received little attention, even though their critical role has been documented in other mammals. Here, the investigators will focus on the role of olfaction in organizing the adaptive responses of the newborn to the mother's breast and of the mother to her baby.

Research data in humans show that: 1) several mammary secretions (colostrum/milk, areolar secretions) emit odorous compounds, and 2) newborns respond to them in a stereotypical and repeatable manner. These odors, which are specific to the mammary gland, serve to facilitate the very first mother-infant interactions. However, the source of these odorous compounds remains unclear, and their chemical nature is unknown. Without precise chemical identification, it is difficult to fully understand the mechanisms by which odors influence the newborn's behavior toward the mother's breast at the start of breastfeeding. Conversely, the newborn's body odors could also convey information about its emotional or metabolic state and influence maternal motivation and behavior.

Based on research conducted on other mammals, as well as studies focused on our own species, the investigators know that: 1) postpartum mothers are highly receptive to the body odor of their newborns, and 2) newborns emit odor compounds that are appreciated by mothers (even if the infants are not their own) . It cannot therefore be ruled out that human mothers react, even unconsciously, to these infant odors and that these odors could help regulate maternal psychophysiology (particularly that underlying lactation and the related chemocommunication mechanisms).

The OD-ALL project aims to unravel the chemical basis of the olfactory interactions that lead to the establishment of the breastfeeding relationship between each member of the mother-newborn dyad. To this end, the investigators will apply an innovative technology, proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), which has previously been used to monitor volatile organic compounds (VOCs) in the environment. Unlike conventional techniques (such as gas chromatography coupled with mass spectrometry; GC-MS), which allow only sporadic and somewhat disruptive measurements, PTR-ToF-MS records odor emissions in real time, without any disruption to the natural interactions taking place. It is capable of providing a true "chemical video" of the dynamic variations in VOCs of mammary or infant origin (whereas conventional GC-MS provides only a "chemical snapshot"). These fluctuations can thus be correlated with the behaviors and physiological responses of mothers and newborns, which will be recorded concurrently. This approach opens up entirely new avenues for understanding the chemosensory foundations of early human interactions, particularly those that occur during the initiation of breastfeeding. Alongside this fundamental approach, the OD-ALL project aims to raise awareness among healthcare professionals, the general public and health policy makers regarding the role of smell in early interactions between mother and newborn.

Inclusion Criteria:

• Regarding mothers:

  • Individuals who have provided their consent (studies 1, 2, and 3) as well as that of their child (studies 1 and 3).
  • Adults.
  • Birth of a singleton newborn.
  • Breastfeeding woman (studies 1 and 2).
  • Absence of any infectious risk and any prior morbidity during pregnancy, childbirth, and breastfeeding (determined by medical staff).

• Regarding newborns:

  • Absence of medical problems during pregnancy, at delivery (full-term birth: 37-42 weeks of amenorrhea, Apgar score > 7 at 1 and 10 minutes; birth weight > 2500 g), or during the neonatal period.

Exclusion Criteria:

• Regarding mothers:

  • Any mother with an infectious disease (HIV, hepatitis A or B) or under special medical supervision.
  • Mothers taking medication that may alter body odor (e.g., corticosteroids, progestins, antidepressants).
  • Mothers who smoke.
  • Mothers suffering from chronic (confirmed congenital anosmia) or acute impairments of the sense of smell (nasal congestion due to infection or allergy).
  • Mothers subject to legal protective measures (guardianship, conservatorship).
  • Mothers subject to judicial protective measures.

• Regarding newborns:

  • Any child who experienced medical problems during pregnancy, childbirth, or the neonatal period (Apgar score < 7 at 1, 5, and 10 minutes).
  • Congenital anosmia (if this information is noted in the medical record; for example, in cases of Du Morsier-Kallman syndrome).

Breastfeeding women who have given birth to a single newborn / who may be accompanied by their newborn