Vernix, also known as vernix caseosa, is a waxy coating which develops on the skin of fetuses, starting around the 20th week of pregnancy. The level of this waxy coating declines over the course of the pregnancy, with full term babies typically having very little vernix, while premature infants may have a thicker layer of this white, waxy substance. Many people remove vernix shortly after birth while wiping the baby down and bathing it, while others advocate leaving it in place.
This substance consists primarily of sebum, which is secreted from glands in the fetus. It is believed to protect the developing fetus from the amniotic fluid, acting as a moisturizer to prevent damage to the skin; anyone who has spent a long time in a bath or the pool has noted what can happen to skin when it is exposed to prolonged moisture. This substance also appears to have antibacterial properties which can reduce susceptibility to infection, which is why some parents prefer to leave it in place to provide extra protection immediately after birth. The moisturizing properties of the coating can also help prevent drying and cracking of infant skin.
Vernix may be waxy to cheesy in texture, and it is typically white, although it may be streaked with birth fluids which cause it to discolor. Different babies can be born with varying amounts of this substance on their bodies, and greater or lesser levels are not a cause for concern. People usually wash the newborn clean because they are concerned about cleanliness, and because they want to avoid smearing birth fluids on clothing and blankets.
Parents are sometimes unprepared for the appearance of vernix, and it can surprise them. Other things which can surprise new parents include deformation of the facial features, caused by passage through the vagina, and the appearance of bruising on the body of the infant. All of these things will naturally resolve themselves within hours or days after birth, although they can be somewhat alarming for those who have never seen a newborn infant before.
For parents who opt to leave the coating on, it will eventually be absorbed into the skin, or it will dry up and flake off over time. Parents may also decide to lightly massage the substance into the skin, providing the baby with some skin to skin contact and preserving the moisturizing properties of the vernix. No harm will be done to an infant by washing or wiping the substance away, however.