What Makes Babies Smile: The Science Behind Your Smile Part 3

The smile of a baby is one of the most coveted smiles. We will make ridiculous faces and noises, dance, sing, or stand on our heads to get a baby to smile. And when the baby smiles, we are absolutely sure that it is an true reflection of how likeable we are and how smart that baby is. But what does a baby’s smile really mean? And when do human smiles begin?

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Infants begin to smile within the very first few weeks of life. The earliest smiles occur during active sleep (a type of sleep unique to babies when much of the brain is activated) and, during the first month, babies will most often smile when sleepy in response to a high-pitched sound (strange, but true) [1]. Babies who are blind have this same pattern of development, providing good evidence that the smile is hard-wired. After the first month, however, an infant begins to smile in response to what they see, and what babies like to see most are faces! Researchers believe that these earliest smiles represent the pleasure of the baby recognizing an object (such as Mommy or Daddy) [2]. By two months, infants begin to develop the smile that communicates their emotional experience of pleasure and contentment. From age two to six months, infants smile more and more often, frequently in response to interaction with a parent or caregiver.


Babies have the same range of types of smiles as adults. They make the Duchenne smile and also the social smile. Do these smiles differ in meaning in the same way as they do in adults? For babies, does the authentic smile indicate happiness while the social smile is doesn’t? It seems that we learn very early to use the social smile. In ten-month-old babies, the Duchenne smile is displayed in response to the smile of their mothers, while babies give a social smile to a stranger. When babies make an authentic smile, the left frontal part of their brains was activated, the same part of the brain that is activated when adults experience happiness [3]. The Duchenne smile appears to be a clear expression of joy and engagement in play with other babies and adults [2].

Babies very quickly develop their own typical facial expressions. By six months old, some babies smile more and some less. These differences seem to be related to the baby’s temperament and affective style [4]. The patterns of individual facial movement, however, are similar in families and appear to be inherited. In a study of congenitally blind adults, researchers compared their facial expressions to those of their family members [5]. They found that the facial expressions of the blind family member were very similar to those of a parent or sibling both in appearance and frequency. It is clear that babies come into this world wired to smile!


  1. Messinger, D.S., Smiling, in The Encyclopedia of Human Development, N.J. Salkind, Editor. 2005, Sage Publications: Thousand Oaks, CA.
  2. Messinger, D.S. and A. Fogel, The interactive development of social smiling, in Advances in Child Development and Behavior, R. Kail, Editor. 2007, Elsevier: Oxford. p. 328-366.
  3. Fox, N.A. and R.J. Davidson, Patterns of brain electrical activity during the expression of discrete emotions in ten-month-old infants. Developmental Psychology, 1988. 24(230-236).
  4. Moore, G.A., J.F. Cohn, and S.B. Campbell, Mothers’ affective behavior with infant siblings: stability and change. Dev Psychol, 1997. 33(5): p. 856-60.
  5. Peleg, G., et al., Hereditary family signature of facial expression. Proceedings of the National Academy of Sciences of the United States of America, 2006. 103(43): p. 15921-15926.
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