vernix

Vernix caseosa, commonly known as vernix, is a white, waxy coating that covers the skin of human fetuses and newborns. The term derives from Latin, referring to a varnish-like cheese.

It begins to form in the second trimester and is typically most abundant in preterm infants, thinning as gestation progresses. It is produced by secretions of sebaceous glands and by desquamated epithelial cells from fetal skin.

Its composition is mainly water, with lipids and proteins providing the protective properties. Lipids include fatty acids and cholesterol; proteins include antimicrobial peptides. The vernix forms a continuous, moisturising barrier on the fetus that is gradually lost after birth.

Functions include protection from the irritant effects of amniotic fluid, lubrication during birth, maintenance of skin hydration, and antimicrobial activity that may support the early establishment of the skin microbiome. It may also contribute to thermal protection in the first hours after birth.

Clinical management varies; vernix is often washed off soon after birth, but many guidelines advocate delaying routine bathing to preserve vernix, particularly for preterm babies, because of potential skin and infection benefits.