Why is the newborn covered in grease?

At first sight, the newborn human baby fresh from the womb is reminiscent of a swimmer about to attempt the English Channel. What the two have in common is a thick covering of whitish grease giving them a strange pasted look. For the swimmer the grease acts as a thermal barrier. For the infant there may be a similar advantage after the delivery is over, the extra coating helping to buffer the newborn against any sudden drop in temperature, but its main function comes earlier, as a lubricant.

Technically the grease is known as the vernix caseosa which means literally the ‘cheesy varnish’. It is formed from a mixture of shed flakes of skin and oily secretions from the sebaceous glands. These glands, which are associated with hair follicles, become unusually active in the last few months of pregnancy, so that by the time of birth they have coated the whole surface of the baby’s body with a slippery layer that eases its passage through the tight birth canal. Without it birth would be almost impossible.

An additional function suggested for the vernix is that it helps the skin of the unborn baby to resist water-logging as it floats in the amniotic fluid, but if this is the case it is surprising that it is only fully developed in the final weeks of the nine months pregnancy. Its special timing strongly favours the lubrication theory.

A secondary function that is more convincing is its role as a defensive barrier against minor skin infections during the vulnerable first few days of life. For this reason, it is sometimes left in place until it falls away naturally, about two or three days following delivery.

For many mothers, however, the idea of having a new baby caked in what has been described as a ‘cream cheese pack’, is slightly offensive and there is a strong urge to have the infant washed clean as soon as possible. This is, indeed, the favoured routine in most places, after which the baby is gently wrapped in soft warm clothing. Given the high levels of hygiene that have become common practice with the newborn today, the risk of increasing its vulnerability to infections because of this cleansing is minimal.