The small, vertical indentation positioned centrally between the base of the nose and the top of the upper lip is a distinct feature of the human face. This subtle groove is a precisely formed anatomical structure with a technical designation. Scientists and medical professionals refer to this feature as the philtrum.
The Philtrum: Name and Anatomy
The philtrum is the vertical groove located in the midline of the upper lip, extending downward from the nasal septum. This central depression is flanked by two elevated ridges known as the philtral columns. These columns converge as they descend, terminating at the tubercle, the slight projection in the center of the upper lip’s vermillion border.
The name “philtrum” originates from the Ancient Greek word phíltron, meaning “love charm” or “love potion.” This reflects the ancient Greek belief that the philtrum was an erogenous spot. While the philtrum exists in many mammals, often helping to channel moisture to the nose, in humans it survives as a vestigial feature with no apparent functional role.
Embryological Origin of the Philtrum
The philtrum’s existence is a consequence of the complex process of facial development that occurs during the first two months of gestation. Facial structures begin to form rapidly around the fourth week of embryonic development. The upper lip and mid-face are built from five different embryonic tissue masses, or prominences, that grow and merge.
The philtrum is formed by the fusion of three specific segments: the two medial nasal prominences and the two maxillary prominences. The medial nasal prominences merge in the midline to form the intermaxillary segment, which contributes the central section of the upper lip, including the philtrum. The maxillary prominences then grow inward to cover the lateral aspects of the medial nasal processes.
This merging process takes place between the fourth and seventh weeks, creating the philtrum as a seam. The groove and its columns represent the final point where separate facial components come together to create a continuous upper lip structure. If this fusion process is incomplete, it can lead to congenital malformations.
Clinical Importance of Philtrum Morphology
The physical appearance of the philtrum is used as a diagnostic indicator for certain developmental conditions. When the three facial segments fail to fuse properly during the embryonic period, the result can be an orofacial cleft, commonly known as a cleft lip. This malformation occurs along the lines of fusion that define the philtrum, highlighting its origin as an anatomical seam.
The philtrum’s shape is also a marker for Fetal Alcohol Spectrum Disorders (FASD). In individuals with FASD, the philtrum is often described as “smooth” or “flattened,” meaning the distinctive vertical ridges are diminished or absent. This smooth philtrum, along with a thin upper lip and short palpebral fissures, is considered one of the three facial features of the disorder.
Clinicians use a five-point pictorial scale called the Lip-Philtrum Guide, to accurately score the degree of smoothness. A flattened philtrum is a sign of underlying issues with cell migration and proliferation during early facial development caused by prenatal alcohol exposure. The presence or absence of a well-defined philtrum provides medical professionals with a non-invasive physical clue to an individual’s developmental history.