[3] In most mammals, the philtrum is a narrow groove that may carry dissolved odorants from the rhinarium or nose pad to the vomeronasal organ via ducts inside the mouth.

[5] The human philtrum, bordered by a pair of ridges known as the philtral columns, is also known as the infranasal depression, but has no apparent function.

[13] In the book Prince Ombra by Roderick MacLeish, the "cleft on our upper lips" is attributed to being hushed by a "cavern angel" just before we are born.

[15] In Les Misérables by Victor Hugo, as translated by Isabel F. Hapgood, Fantine's philtrum is described thus, "in the very characteristic interval which separates the base of the nose from the upper lip, she had that imperceptible and charming fold, a mysterious sign of chastity, which makes Barberousse fall in love with a Diana found in the treasures of Iconia."

[16] In Icelandic folklore, the huldufólk, or elfin "hidden people", may appear as normal humans but have a physical characteristic making them different: they have a convex rather than concave philtrum.