An epicanthic fold, epicanthal fold, or epicanthus is a skin fold

Skin fold

Skin folds are areas of skin where it folds. Many skin folds are distinct, heritable anatomical features, and may be used for identification of animal species, while others are non-specific and may be produced either by individual development of an organism or by arbitrary application of force to...

 of the upper eyelid

Eyelid

An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...

, covering the inner corner (medial canthus

Canthus

The Canthus is either corner of the eye where the upper and lower eyelids meet.Canthus may also refer to:* Canthus of the eye, also called the orbital canthus* Canthus , the sides of the snout in reptiles in amphibians...

) of the eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

.

Other names for this trait include plica palpebronasalis, palpebronasal fold, and Mongolian eye fold.

Factors

One of the primary facial features often closely associated with the epicanthic folds is the nose bridge; all else equal, a lower-based nose bridge is more likely to result in epicanthic folds, and vice versa. There are various factors influencing whether someone has epicanthic folds, including race, age, and certain medical conditions.

Race

Mongoloids are more likely than Caucasoids to retain the epicanthic fold with age, although it varies demographically. Anthropologist Ashley Montagu

Ashley Montagu

Montague Francis Ashley Montagu was a British-American anthropologist and humanist, of Jewish ancestry, who popularized topics such as race and gender and their relation to politics and development...

 wrote in 1988 that for some Mongoloids the "nose is flatter at the root (the miscalled bridge) and the slight fold of skin over the median part of the eye, the Epicanthic fold, is preserved."

Age

Many fetus

Fetus

A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

es lose their epicanthic folds after 3 to 6 months of gestation.

Medical conditions

Medical conditions that cause the nasal bridge to not mature and project are associated with epicanthic folds. One of the characteristics of Down Syndrome

Down syndrome

Down syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The condition was clinically described earlier in the 19th...

 is prominent epicanthic folds.
In Zellweger syndrome

Zellweger syndrome

Zellweger syndrome, also called cerebrohepatorenal syndrome is a rare, congenital disorder, characterized by the reduction or absence of functional peroxisomes in the cells of an individual. It is one of a family of disorders called leukodystrophies...

, epicanthic folds are prominent.
Other examples are fetal alcohol syndrome

Fetal alcohol syndrome

Fetal alcohol syndrome is a pattern of mental and physical defects that can develop in a fetus in association with high levels of alcohol consumption during pregnancy. Current research also implicates other lifestyle choices made by the prospective mother...

, phenylketonuria

Phenylketonuria

Phenylketonuria is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase , rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine...

, and Turner syndrome

Turner syndrome

Turner syndrome or Ullrich-Turner syndrome encompasses several conditions in human females, of which monosomy X is most common. It is a chromosomal abnormality in which all or part of one of the sex chromosomes is absent...

.