Sebum and the Sebaceous Glands

2. Vernix Caseosa

During the last trimester, fetuses develop a sebum-like coating called vernix caseosa. This biofilm helps babies adapt to life inside and outside the uterus. The periderm, a superficial layer of the epidermis that forms in week 11 of pregnancy to protect the fetus while it is in the amniotic fluid, is a component of vernix caseosa -- the shed periderm cells mix with sebum to produce the biofilm. Unlike sebum, the vernix has a lipid composition of only nine percent. More than 80 percent of the mixture is water, and ten percent is proteins.