Vernix caseosa, also known as vernix or birthing custard, is the waxy white substance found coating the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

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

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

, ''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 Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...

, 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 compact ...

; these shedding mix with secretions of sebum by the

sebaceous gland A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...

s to form vernix, which gradually covers the body in an anteroposterior and

dorsoventral 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 ...

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 An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although ...

by increasing concentrations of

pulmonary surfactant Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic In chemistry, hydrophobicity is t ...

s 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 A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest nu ...

, 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 is ...

hair. Chemically, it is water (80%),

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

s (10%) and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s (10%). The lipids include ceramides,

cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as w ...

waxes Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to give low ...

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 A wax ester (WE) is an ester of a fatty acid and a fatty alcohol. Wax esters comprise the main components of three commercially important waxes: carnauba wax, candelilla wax, and beeswax.. Wax esters are formed by combining one fatty acid with o ...

ratio than preterm infants.

Morphology

Vernix is composed of mobile corneocytes 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 corneocytes 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, lactoferrin and antimicrobial components in peptide layer. *Moisturizing the

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 perio ...

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''.

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