Editor’s Note: This article has been updated for clarity, readability, and editorial consistency. The medical information reflects knowledge at the time of original publication and is preserved for historical reference. It is not intended as current medical advice.
Key Takeaways
- Babies notice who shares saliva, like during food sharing, and link it to close relationships.
- They expect support from those they see in these intimate interactions, even without words.
- Social learning starts early, and babies may build a map of who they can trust just by watching.
Babies carefully observe their environment, especially when two people participate in actions where sharing saliva takes place. According to MIT, this allows them to gauge the level of intimacy between people.
Mother With Baby
By nature, humans are social animals, and knowing who we should and should not count on is crucial to the survival of our species. For babies and young children, observing saliva-sharing behaviors, such as kissing or sharing food, may serve as a key signal of close interpersonal relationships. This is the conclusion of a study done at MIT, which suggests that babies use these signals to know who in their environment is most likely to help if a need arises. But how do infants, who cannot yet speak, assess such complex relationships? According to researchers, it’s all in the subtle cues. “Babies are learning about social structures through observation,” said Rebecca Saxe, a cognitive neuroscience professor at MIT and one of the study’s senior authors.
How Babies Use Social Cues to Judge Relationships
The MIT researchers wanted to know whether babies can determine whether there is a strong or weak bond between two individuals. People who are intimately close and share a strong relationship, such as members of a family, a married couple, or siblings, are more likely to share bodily fluids, such as saliva. The question that scientists wanted to have answered was whether this is a clue that babies use to understand their social environment. To answer this question, the researchers looked at how 16- to 18-month-old infants and babies under one year old interact with stuffed animals and dolls.
The researchers designed two controlled behavioral experiments involving 118 infants aged 14.5 to 19 months. In one scenario, an actor visibly shared an orange slice with a puppet—an act involving potential saliva exchange—while another actor engaged in a neutral activity (playing ball). This contrast helped isolate whether the infants responded more to intimacy cues (saliva-sharing) or general social interaction. During a staged emergency, infants predominantly looked toward the actor who had shared food, implying their understanding of stronger social bonds through food (and thus saliva) sharing. In a second test, infants observed an actor place a finger in their mouth (indicating saliva contact) before touching a puppet. Again, during an emergency, the infants anticipated a response from the actor who had previously demonstrated a saliva-based interaction. These findings showed consistent patterns across groups, though more research is needed to confirm how these cues function outside of controlled settings.
Researchers refer to these emotionally close bonds as “thick relationships”—connections defined by strong attachment, mutual care, and shared obligations, such as those found within nuclear families. To explore whether this idea holds up outside the lab, the team also surveyed 129 parents. Most reported they were only comfortable with saliva-sharing behaviors, like utensil sharing or face-kissing, between their child and close family members. This real-world validation suggests that even adults intuitively associate these interactions with deeper emotional closeness.
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FAQs
What was the main goal of the MIT study?
Researchers wanted to see if babies use saliva-sharing behaviors, like food sharing or mouth-touching, to figure out which people have closer relationships.
How was the study done?
Over 100 infants watched actors interact with puppets—some shared food (saliva), others played games. Then, during a “crisis,” researchers observed which actor the baby expected to step in and help.
What did the babies do?
They looked more often at the actor who had shared food or saliva with the puppet, which researchers interpreted as a sign that the infants associated that individual with a stronger social connection.
What age were the babies?
The infants were between 8 and 19 months old—some could crawl or walk, but none could talk yet.
Does this mean babies understand intimacy?
Not exactly. But they seem to recognize patterns in who helps whom, and saliva-sharing stood out as a strong social clue.
Why saliva and not just play?
Because saliva-sharing tends to happen in close relationships, like between family members. Babies seem to pick up on that distinction.
Was it just one experiment?
No, two different experiments were done—one with food-sharing, another with direct saliva contact (a finger in the mouth). Both showed similar results.
Are the findings conclusive?
They’re compelling, but not final. More research is needed to see how these cues work in real-life settings or across different cultures.
What makes this study unique?
It shifts the focus from how babies bond with caregivers to how they observe relationships around them, almost like little social scientists.
Does this change parenting?
Not directly, but it highlights how much babies are watching and learning from everyday interactions—even ones we don’t think twice about.
Final Thought
The idea that babies use saliva-sharing as a signal of intimacy is both intuitive and scientifically intriguing, but it shouldn’t be viewed as the whole story. Social bonding cues are complex, culturally shaped, and context-dependent. In some cultures, close family members may rarely share food or kiss, yet maintain deep emotional ties. Moreover, real-world environments offer many overlapping signals—tone of voice, touch, proximity—that may be just as influential. Could these cues override or reinforce what saliva-sharing suggests? And what about children in non-traditional family structures or those exposed to inconsistent caregiving—do they develop different “social radars”? The study opens an exciting window into early cognition, but it also reminds us to avoid overly simplified interpretations. If anything, it reinforces the remarkable sensitivity babies have to human relationships—and how much we’re only beginning to understand about the foundations of trust and connection.
References
Thomas, A. J., Woo, B. J., Nettle, D., Spelke, E. S., & Saxe, R. (2022). Early concepts of intimacy: Young humans use saliva sharing to infer close relationships. Science, 375(6577), 311–315. https://doi.org/10.1126/science.abh1054
