Waxy white substance found coating the skin of newborn human babies
Newborn baby immediately after birth, covered in vernix
Vernix caseosa, or simplyvernix, is the waxy white substance found coating theskin ofnewborn human babies.[1] It is produced by dedicated cells and is thought to have some protective roles during fetal development and for a few hours after birth.
Vernix is produced during a distinct phase of theepidermal development.[2] Around the 21st week ofgestation, periderm cells are being shed and replaced withstratum corneum; these shedding mix with secretions of sebum by thesebaceous glands to form vernix, which gradually covers the body in ananteroposterior anddorsoventral pattern.[1][2][3] Vernix, in itself, is also believed to aid in the formation of stratum corneum.[4] By early third trimester, the process is complete.[5]
Soon enough, part of the vernix isemulsified by increasing concentrations ofpulmonary surfactants and desiccates, only to be consumed by the fetus; a corresponding increase inamniotic fluid turbidity is noticed.[2]
Vernix has a highly variable makeup but is primarily composed ofsebum, cells that have sloughed off the fetus's skin and shedlanugo hair.[6] Chemically, it is water (80%),lipids (10%) andproteins (10%).[1] The lipids includeceramides,cholesterol,fatty acids,triglycerides,waxes andsterol esters,squalene, andphospholipids;[1] multiple detailed analyses of the polar components have been done.[7] 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.[8]
The protein composition is relatively understudied.[1] Vernix of term infants has moresqualene and a higherwax ester tosterol ester ratio than preterm infants.[6]
Vernix is composed of mobilecorneocytes embedded in an amorphous lipid matrix.[1] Precise biological mechanisms leading to its formation are poorly understood.[9]
The cells are polygonal or ovoid in shape, malleable, and lack nuclei; typical thickness is 1-2 μm.[1] Nuclear ghosts are frequently observed and Acid Phosphatase Activity is nonuniform.[1] Keratin filaments build a scaffold like structure which form a water-storage area.[1] As opposed to stratum corneum, the vernixcorneocytes lack desmosomal attachment and the lipid layer is more disordered.[10]
Vernix is a white viscous cream-like substance in appearance.[1]
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.[1][11][12]
Vernix appears in allfull-term infants, with widely varying body coverage. Premature and post-mature births generally do not display any.[6][2][13]
It is theorized (and observed) to serve several purposes:[1][2][11]
Waterproofing the skin while in gestation
Lubricating the infant's skin and facilitating easy passage through thebirth canal
Preventing infections — primarily as a mechanical barrier and secondarily via the presence oflysozyme,lactoferrin, and antimicrobial components in the peptide layer
Vernix is used as a reliable site-of-record for measuring cocaine exposure in pregnant women.[2][15] Using vernix for diagnosing uterine rupture andamniotic fluid embolism has been proposed.[2]
Vernix was thought to be unique to human fetal development. In 2018, vernix-like material was reportedly obtained from pups of theCalifornia sea lion.[16] 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.[17]
^Moore AL, Marshall CD, Nauta A, Lorenz HP,Longaker MT (2019-01-01). "Chapter 5 - Scarless Wound Healing: From Experimental Target to Clinical Reality". In Atala A, Lanza R, Mikos AG, Nerem R (eds.).Principles of Regenerative Medicine (Third ed.). Boston: Academic Press. pp. 65–92.doi:10.1016/B978-0-12-809880-6.00005-9.ISBN978-0-12-809880-6.S2CID81194374.
^Hoath SB, Shah KN (2017-01-01). "49 - Physiologic Development of the Skin". In Polin RA, Abman SH, Rowitch DH, Benitz WE (eds.).Fetal and Neonatal Physiology (Fifth ed.). Elsevier. pp. 498–514.e4.doi:10.1016/B978-0-323-35214-7.00049-4.ISBN978-0-323-35214-7.
^Karperien M, Roelen BA, Poelmann RE, Gittenberger-de Groot AC, Hierck BP, DeRuiter MC, Meijer D, Gibbs S (2015-01-01). "Chapter 3 - Tissue Formation during Embryogenesis". In Blitterswijk CA, De Boer J (eds.).Tissue Engineering(PDF) (Second ed.). Oxford: Academic Press. pp. 67–109.doi:10.1016/B978-0-12-420145-3.00003-1.ISBN978-0-12-420145-3. Archived fromthe original(PDF) on 2023-12-14. Retrieved2023-11-27.
^abcSchachner LA, Hansen RC (2003).Pediatric dermatology. St. Louis: Mosby. pp. 206–7.ISBN978-0-323-02611-6.
^Hoath SB, Narendran V, Visscher MO (2011). "Vernix Caseosa and Innate Immunity".Innate Immune System of Skin and Oral Mucosa. John Wiley & Sons, Ltd. pp. 145–169.doi:10.1002/9781118025338.ch8.ISBN978-1-118-02533-8.
