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Vernix caseosa, also known as vernix or birthing custard, is the waxy white substance found coating the skin of newborn human babies. 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''.


In-utero development

Vernix is produced during a distinct phase of the epidermal development. Around the 21st week of gestation, periderm cells are being shed and replaced with
stratum corneum The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compac ...
; these shedding mix with secretions of sebum by the sebaceous glands to form vernix, which gradually covers the body in an
anteroposterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
and dorsoventral pattern. Vernix, in itself, is also believed to aid in the formation of stratum corneum. By early third trimester, the process is complete. 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 The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products betwee ...
turbidity is noticed.


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 Lanugo is very thin, soft, usually unpigmented, downy hair that is sometimes found on the body of a fetus or newborn. It is the first hair to be produced by the fetal hair follicles, and it usually appears around sixteen weeks of gestation and i ...
hair. Chemically, it is water (80%), lipids (10%) and proteins (10%). The lipids include
ceramide Ceramides are a family of waxy lipid molecules. A ceramide is composed of N-acetylsphingosine and a fatty acid. Ceramides are found in high concentrations within the cell membrane of eukaryotic cells, since they are component lipids that make u ...
s, cholesterol, fatty acids, triglycerides, waxes and
sterol ester Sterol esters are a heterogeneous group of chemical compounds. They are created when the hydroxyl group of a sterol and a fatty acid undergo an esterification reaction. They can be found in trace amounts in every cell type but are highly enriched i ...
s, squalene, and
phospholipid Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...
s; multiple detailed analyses of the polar components have been done. The protein composition is relatively understudied. Vernix of term infants has more squalene and a higher wax ester to
sterol ester Sterol esters are a heterogeneous group of chemical compounds. They are created when the hydroxyl group of a sterol and a fatty acid undergo an esterification reaction. They can be found in trace amounts in every cell type but are highly enriched i ...
ratio than preterm infants.


Morphology

Vernix is composed of mobile
corneocyte Corneocytes are terminally differentiated keratinocytes and compose most of the stratum corneum, the outermost layer of the epidermis. They are regularly replaced through desquamation and renewal from lower epidermal layers and are essential for ...
s embedded in an amorphous lipid matrix. Precise biological mechanisms leading to its formation are poorly understood. The cells are polygonal or ovoid in shape, malleable, and lack nuclei; typical thickness is 1-2 µm. Nuclear ghosts are frequently observed and Acid Phosphatase Activity is nonuniform. Keratin filaments build a scaffold like structure which form a water-storage area. As opposed to stratum corneum, the vernix
corneocyte Corneocytes are terminally differentiated keratinocytes and compose most of the stratum corneum, the outermost layer of the epidermis. They are regularly replaced through desquamation and renewal from lower epidermal layers and are essential for ...
s lack desmosomal attachment and the lipid layer is more disordered.


Physical properties

Vernix is a white viscous cream-like substance in appearance. 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.


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. It is theorized (and observed) to serve several purposes: * Waterproofing the skin, whilst in gestation. * Lubricating the infant's skin, and facilitating easy passage through the
birth canal In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
. *Preventing infections — primarily as a mechanical barrier and secondarily via the presence of
lysozyme Lysozyme (EC 3.2.1.17, muramidase, ''N''-acetylmuramide glycanhydrolase; systematic name peptidoglycan ''N''-acetylmuramoylhydrolase) is an antimicrobial enzyme produced by animals that forms part of the innate immune system. It is a glycoside ...
,
lactoferrin Lactoferrin (LF), also known as lactotransferrin (LTF), is a multifunctional protein of the transferrin family. Lactoferrin is a globular glycoprotein with a molecular mass of about 80 kDa that is widely represented in various secretory fluids, ...
and antimicrobial components in peptide layer. *Moisturizing the
stratum corneum The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compac ...
whilst in gestation (and controlled drying in
post-partum The postpartum (or postnatal) period begins after childbirth and is typically considered to end within 6 weeks as the mother's body, including hormone levels and uterus size, returns to a non-pregnant state. The terms puerperium, puerperal peri ...
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).


Medical uses

Vernix is used as a reliable site-of-record for measuring cocaine exposure in pregnant women. Using vernix for diagnosing uterine rupture and amniotic fluid embolism has been proposed.


Disorders

Granuloma and peritonitis of vernix have been observed in
Caesarean section Caesarean section, also known as C-section or caesarean delivery, is the surgical procedure by which one or more babies are delivered through an incision in the mother's abdomen, often performed because vaginal delivery would put the baby or mo ...
s. High volumes of vernix cause Neonatal Aspiration Syndrome.


Other species

Vernix is thought to be unique to human fetal development; in 2018, vernix-like material was reportedly obtained from pups of ''
Zalophus californianus The California sea lion (''Zalophus californianus'') is a coastal eared seal native to western North America. It is one of six species of sea lions. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of Califo ...
''.


Additional images

Vernix feet.jpg, Vernix on a newborn's legs and feet. Newborn minutes after delivery.jpg, Traces of ''vernix caseosa'' on a full term newborn. Postpartum baby3.jpg, Closeup of baby's face right after birth, skin covered in vernix and some blood.


References


External links

{{commons category Immune system Neonatology Skin