[7][8][9] Various factors influence whether epicanthic folds form, including ancestry, age, and certain medical conditions.

Epicanthus means 'above the canthus', with epi-canthus being the Latinized form of the Ancient Greek ἐπί κανθός: 'corner of the eye'.

Among South Asians, they occur at very high frequencies among the Nepalis, Bhutanese,[11][better source needed] Northeast Indians,[11] Kirati people and certain Adivasi[11] tribes of Eastern and Southern India.

[12] Epicanthic folds also occur, at a considerably lower frequency, in other populations: Europeans (e.g., Scandinavians, English, Irish,[13] Hungarians, Russians, Poles, Lithuanians, Latvians, Finns, Estonians and Samis),[14][15] Jews, South Asians (Bengalis,[11] Sinhalese,[16] among other groups in eastern and southern South Asia),[11] Nilotes, Cushites, and Amazigh people.

Dr. Frank Poirier, a physical anthropologist at Ohio State University, said that the epicanthic fold among Asian people is often explained as part of an adaptation to severe cold or tropical environments, however he suggests that neither of these explanations are sufficient to explain its presence in East and Southeast Asia, and notes that the fold can also be observed in Irish and African people.

Medical conditions that cause the nasal bridge not to develop and project are also associated with epicanthic fold.