philtrum

The philtrum is the vertical groove in the midline of the upper lip, extending from the base of the nose to the border of the vermilion. It is bordered by two raised ridges on either side, known as the philtral columns or ridges.

It forms during embryonic development when the medial nasal processes fuse with the maxillary prominences. This fusion occurs in the first trimester, typically between the 6th and 10th weeks of gestation. Proper fusion yields a centered philtrum, while failure or disruption of fusion can contribute to or accompany cleft lip and/or cleft palate.

In the general population, the philtrum varies in depth, length, and shape. A smooth or unusually short philtrum can be associated with certain developmental conditions, most notably fetal alcohol spectrum disorders, where standardized assessment tools such as the Lip-Philtrum Guide are used. However, a smooth philtrum is not diagnostic on its own and can occur for other reasons.

The philtrum's exact biological function is not clearly established; it is primarily described as an anatomical feature resulting from fetal facial development. It serves as a recognizable midfacial landmark in clinical examination and anthropological descriptions.