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.