The term “Mongolian eyes” is an outdated and problematic phrase. It is no longer considered acceptable in medical or respectful conversation due to its association with a discredited classification system. This article explains the epicanthic fold, the anatomical characteristic the term once referred to, its prevalence, and its historical misassociation with certain medical conditions.
The Epicanthic Fold Explained
The epicanthic fold, or epicanthus, is a skin fold of the upper eyelid that extends from the nose side of the eye and covers the inner corner, also called the medial canthus. The presence and prominence of these folds are influenced by eyelid structure and surrounding facial bones.
This is a normal and common feature in many human populations worldwide. It is observed with high frequency in individuals of East Asian, Southeast Asian, Central Asian, and North Asian descent, with some estimations suggesting it is present in up to 90% of adults in certain East Asian groups. The epicanthic fold also occurs commonly in Indigenous peoples of the Americas, Polynesians, Micronesians, and some African populations, such as the Khoisan. Epicanthic folds are also common in infants and young children of all ethnic backgrounds. For many non-Asian children, these folds often lessen or disappear as the nasal bridge develops and the face matures, typically by around six years of age.
Association with Medical Conditions
While normal for many, the epicanthic fold can also be associated with certain genetic conditions. Most notably, individuals with Down syndrome, also known as Trisomy 21, frequently exhibit prominent epicanthic folds, with approximately 60% of affected individuals having this feature. Other conditions like Fetal Alcohol Syndrome, Turner syndrome, and Noonan syndrome can also include epicanthic folds among their characteristics.
The historical connection between this feature and Down syndrome led to the scientifically baseless term “mongolism” or “Mongolian idiocy.” In 1862, physician John Langdon Down mistakenly used this terminology based on a perceived facial resemblance to people of “Mongolian race.” This racial classification of developmental disabilities was scientifically disproven and formally deprecated by genetic experts in 1961 due to its misleading connotations. The term is now considered offensive and is no longer used in medical or respectful contexts.
Distinguishing from Mongolian Spots
It is important to distinguish the epicanthic fold from “Mongolian spots,” which are a different dermatological feature. Mongolian spots, medically known as congenital dermal melanocytosis, are harmless, flat birthmarks that appear as blue, blue-gray, or blue-black areas of discoloration on an infant’s skin. They are likened to bruises due to their color and have irregular borders.
These birthmarks are most commonly found on the lower back and buttocks, though they can also appear on the shoulders, limbs, or, less frequently, the face. Mongolian spots are highly prevalent in infants of East Asian, Native American, Hispanic, and African descent, with some studies reporting incidence rates of 81% to 100% in Asian populations and 95.5% to 96% in Black populations. They are caused by melanocytes, pigment-producing cells, becoming trapped deeper in the skin during embryonic development. These spots are benign and usually fade or disappear by early childhood, by one to six years of age, and do not require treatment.