We analyzed 51 primiparous mothers’ data. All participants continued breastfeeding their 2-to-9-month-old infants during the study period. None reported currently having any psychiatric disorders or taking any medication. After the informed consent, we provided a 15-minute get-acquainted period during which mothers did not touch their infants. Then we collected saliva samples, conducted a questionnaire about affect, and conducted two emotion recognition tasks twice, both before and after the manipulation. During the manipulation phase, participants either breastfed or held their infants for 15 minutes. We randomly assigned our participants to either of the two conditions (breastfeeding or holding) and informed them of the same in advance. Finally, the mothers completed all the remaining questionnaires. Since mothers conducted the experiment alone in the sound proof room, fathers and grandmothers of the infants also joined the experiment to care for the infants along with our research assistant. All of the emotion recognition task performances were subtracted pre manipulation scores from post manipulation scores.

Breastfeeding behaviors can significantly change mothers’ physiological and psychological states. The hormone oxytocin may mediate breastfeeding and mothers’ emotion recognition. This study examined the effects of endogenous oxytocin fluctuation via breastfeeding on emotion recognition in 51 primiparous mothers. Saliva oxytocin was assessed before and after the manipulation (breastfeeding or holding an infant), and emotion recognition tasks were conducted. Among mothers who breastfed daily, mothers with more increased levels of oxytocin after breastfeeding showed greater reduced negative recognition and enhanced positive recognition of adult facial expressions. These oxytocin functions accompanying breastfeeding may support continued nurturing behaviors and also affect the general social cognition of other adults beyond any specific effect on infants.