Natural odour preferences of newborn infants change over time.

At their first sucking contact, neonates prefer an unwashed breast to a washed one, but an amniotic fluid (AF)- treated breast over a "natural odour" breast. We examined the development of these neonatal olfactory preferences. On days 3-4 significantly more babies still selected their mother's unwashed breast (n = 21) than the washed alternative (n = 8). Preferences for natural breast odours were more pronounced for girls than boys. In a subsequent experiment comprising another 28 babies, the number of babies who selected a naturally scented (n = 9) vs an AF-treated breast (n = 19) on days 2-5 were not reliably different. However, babies who selected the natural breast had longer pre-test maternal contact and had spent more time breastfeeding. Ten babies who chose the AF breast in the latter experiment were tested in the same manner several days later; all preferred the naturally smelling breast. While preferences for AF fade after birth, responsiveness to natural breast odours may be enhanced by postnatal experience.