Vernix caseosa
Vernix caseosa, or simply vernix, is the waxy white substance found coating the skin of newborn human babies.<ref name=":0">Template:Cite journal</ref> It is produced by dedicated cells and is thought to have some protective roles during fetal development and for a few hours after birth.
Etymology
In Latin, vernix means varnish and caseosa means cheesy. The term was first published in 1846 in the Dunglison Dictionary of Medical Sciences.<ref name=":0" />
In-utero development
Vernix is produced during a distinct phase of the epidermal development.<ref name=":1" /> Around the 21st week of gestation, periderm cells are being shed and replaced with stratum corneum; these shedding mix with secretions of sebum by the sebaceous glands to form vernix, which gradually covers the body in an anteroposterior and dorsoventral pattern.<ref name=":0" /><ref name=":1" /><ref>Template:Cite book</ref> Vernix, in itself, is also believed to aid in the formation of stratum corneum.<ref>Template:Cite book</ref> By early third trimester, the process is complete.<ref>Template:Cite book</ref>
Soon enough, part of the vernix is emulsified by increasing concentrations of pulmonary surfactants and desiccates, only to be consumed by the fetus; a corresponding increase in amniotic fluid turbidity is noticed.<ref name=":1" />
Characteristics
Composition
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.<ref name = Schachner2003>Template:Cite book</ref> Chemically, it is water (80%), lipids (10%) and proteins (10%).<ref name=":0" /> The lipids include ceramides, cholesterol, fatty acids, triglycerides, waxes and sterol esters, squalene, and phospholipids;<ref name=":0" /> multiple detailed analyses of the polar components have been done.<ref>Template:Cite journal</ref> The total fatty acid profile in vernix (either as part of lipids or as fatty acids) contains a variety of less common fatty acids, such as omega-7 polyunsaturated fatty acids or non-methylene-interrupted omega-3 fatty acids.<ref>Template:Cite journal</ref>
The protein composition is relatively understudied.<ref name=":0" /> Vernix of term infants has more squalene and a higher wax ester to sterol ester ratio than preterm infants.<ref name="Schachner2003" />
Morphology
Vernix is composed of mobile corneocytes embedded in an amorphous lipid matrix.<ref name=":0" /> Precise biological mechanisms leading to its formation are poorly understood.<ref>Template:Cite book</ref>
The cells are polygonal or ovoid in shape, malleable, and lack nuclei; typical thickness is 1-2 μm.<ref name=":0" /> Nuclear ghosts are frequently observed and Acid Phosphatase Activity is nonuniform.<ref name=":0" /> Keratin filaments build a scaffold like structure which form a water-storage area.<ref name=":0" /> As opposed to stratum corneum, the vernix corneocytes lack desmosomal attachment and the lipid layer is more disordered.<ref>Template:Cite journal</ref>
Physical properties
Vernix is a white viscous cream-like substance in appearance.<ref name=":0" />
The water is not uniformly distributed throughout, but rather exclusively present in the sponge-like corneocytes; despite its high water content, vernix is non-polar (due to lipids) and more vapor-permeable than stratum corneum.<ref name=":0" /><ref name="nskin">Template:Cite book</ref><ref>Template:Cite journal</ref>
Functions
Vernix appears in all full term infants but with widely varying body-coverage, while premature and post-mature births generally do not display any.<ref name="Schachner2003" /><ref name=":1" /><ref>Template:Citation</ref>
It is theorized (and observed) to serve several purposes:<ref name=":0" /><ref name=":1">Template:Cite journal</ref><ref name="nskin" />
- Waterproofing the skin, whilst in gestation.
- Lubricating the infant's skin, and facilitating easy passage through the birth canal.
- Preventing infections — primarily as a mechanical barrier and secondarily via the presence of lysozyme, lactoferrin and antimicrobial components in peptide layer.
- Moisturizing the stratum corneum whilst in gestation (and controlled drying in post-partum phase).
- Thermoregulation in post-partum phase — evidence is mixed.
- Quick healing of epidermal wounds.
- Development of gut, after intra-uterine consumption.
Electrical isolation of the fetus is also thought to occur due to vernix caseosa (this could affect accurate fECG measurement of fetal heartbeat).<ref>Template:Cite journal</ref>
Medical uses
Vernix is used as a reliable site-of-record for measuring cocaine exposure in pregnant women.<ref name=":1" /><ref>Template:Cite journal</ref> Using vernix for diagnosing uterine rupture and amniotic fluid embolism has been proposed.<ref name=":1" />
Disorders
Granuloma and peritonitis of vernix have been observed in Caesarean sections.<ref name=":1" /> High volumes of vernix cause Neonatal Aspiration Syndrome.<ref name=":1" />
Other species
Vernix was thought to be unique to human fetal development. In 2018, vernix-like material was reportedly obtained from pups of the California sea lion.<ref>Template:Cite journal</ref> Mass spectrometry of the material showed it to be fundamentally the same as human vernix, in both BCFA (branch-chain fatty acids) and squalene content. The presence of vernix throughout the infant gastro-intestinal tract, as well as in the meconium (first excretion), in both human and sea lion neonates, argues that the function of vernix may not be as an external skin protection, as often described in the literature, but as a preparation of the newborn GI tract against water-borne bacteria. As such, vernix caseosa, not present in any terrestrial mammal, including other primates, is one of several arguments for a possible semi-aquatic past of our ancestors.<ref>Template:Cite journal</ref>
Additional images
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Vernix on a newborn's legs and feet. -
Traces of vernix on a full term newborn. -
Closeup of baby's face right after birth, skin covered in vernix and some blood.
