The newborn senses in perspective
Compared to vision and hearing, the chemical senses--taste and smell--seem relatively unimportant.
But for newborns, odors and flavors may transmit crucial information about the world. In fact, new babies may be especially sensitive to the smells and flavors they encounter.
Newborns can recognize the smell of their own amniotic fluid. And they seem primed to learn very quickly about the smells associated with their mothers.
Is this about finding food? Or bonding to their parents? Probably a bit of both. Check out these discoveries about the newborn senses of taste and smell.
What newborns can taste
Researchers recognizes five primary tastes--sweetness, saltiness, bitterness, sourness and umami, a savory, hearty taste associated with glutamate and found in meats, milk products, and mushrooms.
A newborn senses all of these tastes except one: Experiments suggest that babies can’t taste salt until they are about 4 months old (Beauchamp et al 1986).
But newborns love sugar solutions--the sweeter, the better. In fact, when babies are given a sugar solution immediately before a painful procedure--like a heel prick--they cry less. Newborns also seem to like the taste of glutamate, which is found in breast milk (Beauchamp and Pearson 1991).
By contrast, newborns react negatively to some (but not all) bitter substances. And when a newborn senses a sour substance, he is likely to pull away and grimace (Steiner 1977).
Do newborns know about other, more complex flavors? Flavor complexity--what permits us to tell the difference between, say, peaches and apricots--depends on a food’s odor. So if newborns are sensitive to complex flavors, it’s because they have a well-developed sense of smell.
What newborns smell
Scent-memories of the womb
Experiments show that newborns recognize, and are soothed by, the smell of amniotic fluid. In fact, hours after birth, babies prefer breasts that have been dabbed with amniotic fluid (Varendi et al 1997).
This preference fades away after a few days, however. And even while it persists, newborns are also highly attracted to natural breast odors.
Find that breast
In one experiment, researchers tested newborns by holding a pad carrying maternal breast odors 17 centimeters from the baby’s nose. In response, the babies wriggled towards the pad (Varendi and Porter 2001).
Similar methods reveal that babies can distinguish between breast milk and baby formula. When presented with two scents--the scent of non-familiar breast milk and the scent of familiar formula milk--formula-fed newborns showed a preference for the odor of human milk (Marlier and Schaal 2005).
Newborns learn to recognize their own mothers’ distinctive scents
Can newborn babies identify their mothers on the basis of odor alone? It seems that they can. A recent study found that newborns undergoing a painful procedure (a heel prick) were soothed by the smell of breast milk...but only if the milk was from their own mothers (Nishitani et al 2009).
Newborns also respond to breast milk by making mouthing movements. In one experiment, newborns were presented with the odors of different breast milk samples--samples donated by their mothers and by other, unfamiliar women. The babies mouthed more in response to their own mothers’ odors (Mizuno et al 2004).
Interestingly, the effect depended on how much skin-to-skin contact the infants had experienced with their mothers immediately after birth. Those who’d experienced more than 50 minutes of contact showed a greater difference in mouthing (Mizuno at al 2004). The results are consistent with the idea that newborns are especially likely to learn about odors in the minutes immediately after birth.
Is there a sensitive period for olfactory learning in newborns?
Maybe. Romantshik and colleagues presented newborns with a novel odor for 30 minutes starting either
• 4-37 minutes after birth or
• 12 hours after birth
A few days later, the infants were tested on their ability to recognize the odor. Only the babies who’d been exposed to the scent in the first few minutes after birth could do so (Romantshik et al 2007).
In fact, it seems that newborns can acquire preferences for a variety of novel odors if they encounter them immediately after birth.
In one experiment, researchers exposed newborns to the scent of chamomile while they were nursing. Days later, their attraction to the scent of chamomile was as strong as their attraction to the scent of breast milk (Delaunay-El Allam et al 2006).
What else can newborns do?
Quite a bit. The newborn senses of hearing and vision aren't fully developed. Yet babies can recognize their mothers' voices at birth, and they can quickly learn to recognize the faces of their caregivers. For more information about these newborn senses, see my article about social world of newborns.
References: Newborn senses
Beauchamp, G K and Pearson, P.1991. Human development and umami taste. Physiol Behav. 49(5):1009-12.
Beauchamp GK, Cowart BJ, Moran M. Developmental changes in salt acceptability in human infants. Dev. Psychobiology 1986; 19:17-25.
Delaunay-El Allam M, Marlier L, and Schaal B. 2006. Learning at the breast: preference formation for an artificial scent and its attraction against the odor of maternal milk. Infant Behav Dev. 29(3):308-21.
Marlier L and Schaal B. 2005. Human newborns prefer human milk: conspecific milk odor is attractive without postnatal exposure. Child Dev. 76(1):155-68.
Mizuno K, Mizuno N, Shinohara T, and Noda M. 2004. Mother-infant skin-to-skin contact after delivery results in early recognition of own mother's milk odour. Acta Paediatr. 93(12):1640-5.
Nishitani S, Miyamura T, Tagawa M, Sumi M, Takase R, Doi H, Moriuchi H, and Shinohara K. 2009. The calming effect of a maternal breast milk odor on the human newborn infant. Neurosci Res. 63(1):66-71.
Porter RH, Makin JW, Davis LB, Christensen KM. 1991. An assessment of the salient olfactory environment of formula-fed infants. Physiol Behav. 50(5):907-11.
Romantshik O, Porter RH, Tillmann V, Varendi H. 2007. Preliminary evidence of a sensitive period for olfactory learning by human newborns. Acta Pædiatrica. 96( 3):372 - 376.
Steiner JE. 1977. Facial expressions of the neonate infant indicate the hedonics of food - related chemical stimuli. In: Weiffenbach, J.M. (ed): Taste and Development: The Genesis of Sweet Preference. Washington, D.C., U.S. Government Printing Office.
Varendi H, Porter RH, Winberg J. 1996. Attractiveness of amniotic fluid odor: evidence of prenatal olfactory learning? Acta Paediatr. 85(10):1223-7.
Varendi H and Porter RH. 2002. The effect of labor on olfactory exposure learning within the first postnatal hour. Behav Neurosci. 116(2):206-11.
Content last modified 5/11
Image of sleeping newborn by Andres Nieto Porras / wikimedia commons