An assessment of the salient olfactory environment of formula-fed infants.

Olfactory preferences of two-week-old bottle-fed infants were assessed in a series of simultaneous two-choice tests. Infants of each sex displayed preferential orientation to a stimulus pad worn on their mother's breast over a clean control pad. When maternal breast odor was paired with the odor of the infants' formula, however, boys spent more time oriented toward the formula odor, whereas girls evinced no reliable preferences. Although the subject infants had no prior direct contact with odors emanating from the breasts of lactating females, but had recurring reinforced exposure to the odor of their familiar formula (in the context of feeding), the former scents elicited a more positive response. Preferential orientation to lactating-breast odors reflects adaptive inborn attraction to cues associated with the natural food source for human neonates.