Bumpy nipple smells guide babies to milk

YOU may not wonder why women have bumps around their nipples but it has bemused many. Now the mystery has been solved. Smelly secretions released from the nipples of women who have just given birth may help babies find and extract their mother's milk.

During pregnancy, women often notice an increase in the number of bumps, or areolar glands, on the pigmented skin surrounding the nipple - some notice small amounts of secretions from them. It had been assumed that this fluid was to help lubricate the skin, but now it seems it may also contain odoursome molecules that help an infant to find its way to the breast.

Benoist Schaal of the National Centre for Scientific Research in Dijon, France, and his colleagues counted the number of areolar glands on the nipples of 121 new mothers in the first three days after birth, and recorded their babies' sucking performance, body weight, and the time it took for the women to start lactating.

Women with more than nine glands per breast started lactating sooner than those with fewer glands, and their babies gained weight faster. The effect was greater in first-time mothers, who began lactating an average of 10 hours earlier than those with fewer glands. Their infants also fed more frequently (Early Human Behaviour, DOI: 10.1016/j.earlhumdev.2011.07.020).

"The breastfeeding relationship is less easy to establish for first-time mothers bearing low amounts of areolar glands," says Schaal, who adds that babies of first-time mothers may be more reliant on olfactory cues as their mothers are less familiar with other signals that their infant wants to feed.

Schaal's team also found that three-day-old infants exhibit more head and mouth movements related to feeding, such as sucking and licking, when they smell gland secretions, compared with other odours from the human breast - including that of milk itself (PLoS One, DOI: 10.1371/journal.pone.0007579).

Olfactory cues are already known to help other mammals, such as rabbits, to find the breast.

"The finding is important, but might be only one factor among [many] enhancing breastfeeding," says Heili Varendi of the University of Tartu in Estonia, who discovered that newborns prefer to feed from an unwashed breast than a recently cleaned one.

Schaal believes his discovery could have practical implications. If the factors responsible could be extracted, these could be used to help train the mouth muscles of babies who are temporarily unable to breastfeed due to prematurity or illness, so they do better when introduced to the breast. "It could help to prepare them for the transition from tube-feeding to direct sucking on the nipple of the mother or a bottle," says Schaal.

The findings also add support to the existence of pheromone-like compounds in humans. A previous study found that the sexual desire of women is boosted by odours given off by breastfeeding women. "Finding olfactory ways of communication between human newborns and mothers would be a strong demonstration that olfaction is still functional in the human social context," he adds.