Vernix caseosa

Vernix caseosa, also known as vernix, is the waxy or cheese-like white substance found coating the skin of newborn human babies.

In Latin, vernix means varnish and caseosa means cheesy.

Vernix has a highly variable makeup but is primarily composed of sebum, cells that have sloughed off the fetus's skin and shed lanugo hair. 12% of the dry weight of vernix is composed of branched chain fatty acids,cholesterol and ceramide. Vernix of term infants has more squalene and a higher wax ester to sterol ester ratio than preterm infants.

Comparison of lipid components of vernix caseosa, stratum corneum and skin surface (sebaceous):

Amino acid composition of vernix caseosa:

Cells of vernix are typically polygonal or ovoid in shape and lack nuclei. Nuclear ghosts are frequently observed. Vernix corneocytes lack desmosomal attachment and this distinguishes them from corneocytes found in mature stratum corneum. Thickness of a corneocyte is 1-2 µm. These cells are surrounded by a layer of amorphous lipids lacking typical lamellar architecture present in mature stratum corneum.

Vernix is not uniformly distributed, but rather present in form of cellular sponges. The critical surface tension of vernix is 39 dyne/cm. Despite its water content (82%), vernix is nonpolar. These features point towards the "waterproofing" function of vernix, thereby preventing heat loss soon after birth.

Vernix provides electrical isolation for the fetus, which is presumably an important aspect of developing fetal anatomy. Early scientific studies indicated increased evaporative heat loss in infants when vernix was removed soon after birth; but newer reports confirm that washing skin surface after birth reduces evaporative water losses compared to surface of newborns in which vernix is left in situ. Vernix is hydrophobic. Vernix is believed to assist in the development of the human intestinal microbiota.

The sebum in vernix is produced in utero by the sebaceous glands around the 20th week of gestation. Vernix appears primarily in full term infants, while premature and postmature births generally lack any. Postdates desquamation (flakey skin in babies born >42 weeks) is thought to be due to loss of vernix.

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