The Importance of Maternal Kisses

This sculpture by Paul Lancz from 2014 is one of the many public works of art always on display in the city of Montreal. Entitled “La Tendresse/ Tenderness,” it captures a ubiquitous display of affection between mother and child. This physical gesture of a mother kissing her baby has been a hallmark of affection uniting humans across time.

In fact, the maternal kiss is not limited to humans — most barnyard maternal mammals also kiss their infant offspring, although to us it looks like licking. And this fact takes us to evolutionary history — some of the oldest stories of humankind. Mammals invest an extraordinary amount of time nurturing their offspring compared to other species, and humans especially so. The care mothers have for their babies is heartfelt, but the physical expressions of affection are driven partly out of instinct — a mother’s kiss is also a highly sophisticated dance with her baby’s immune system.

Human infants are born with a basic immune system — the innate immune system. But we have to develop our resistance to specific pathogens over time, with contact — this is our adaptive immune system. Once we have antibodies of whatever bacteria or virus that threatens us in our system, we can fight off illnesses. This can leave babies much more vulnerable to infection, and this is where the kiss comes in. When a mother kisses her infant, she samples many pathogens on her baby’s face, and takes them into her own body. Then, the mother’s antibody-producing “B-cells” are activated, and they travel into her breast milk, where the baby can ingest them and gain some immunity. The type of antibody featured in breast milk is called IgA, and it is especially effective for the mucus membranes — the respiratory system and the digestive tract. This makes perfect sense, since the baby swallows so many pathogens!