The philtrum is the vertical groove between the nose and the upper lip. This distinct indentation, bordered by two subtle ridges, varies in depth and prominence among individuals. Its purpose often prompts questions about its origins and function.
Anatomy and Formation
The philtrum is precisely located in the midline of the upper lip, extending upwards to the base of the nose. This vertical groove is flanked by two elevated ridges, known as philtral columns, which define its characteristic appearance. The lower end of the philtrum contributes to the central part of the Cupid’s bow of the upper lip.
This facial structure develops during the early stages of embryonic growth, specifically between the fourth and seventh weeks of gestation. During this period, several facial prominences, including the paired medial nasal processes and the maxillary processes, grow and eventually merge. The medial nasal processes fuse together in the midline, forming the intermaxillary segment, which gives rise to the philtrum and a portion of the primary palate.
Proper fusion of these embryonic structures is essential for the philtrum’s formation. The maxillary processes contribute to the lateral parts of the upper lip, while the medial nasal processes form the central philtrum. This process ensures the integrated formation of the upper lip and central facial region.
Addressing its Function
For humans, the philtrum has no known active function. It is considered a vestigial structure, a remnant of an anatomical feature that had a more defined purpose in ancestral species. In humans, its original function has largely been lost.
In most other mammals, such as dogs and cats, the philtrum is a narrow groove that carries dissolved odorants from the wet nose pad (rhinarium) to the mouth. This aids their sense of smell through capillary action, as a wet nose pad traps odor particles more effectively. However, this mechanism is no longer present in humans.
Some popular beliefs suggest the philtrum contributes to facial expressions or communication, but scientific evidence does not support these claims. While it is part of the overall facial structure involved in expression, it has no unique, active role. Its continued presence is due to its integral role in embryonic facial development rather than any ongoing functional necessity.
Insights from Development
While the philtrum has no active function in adult humans, its formation during embryonic development holds medical relevance. Anomalies in philtrum development can indicate underlying health conditions or developmental syndromes. The philtrum’s appearance, specifically its smoothness or length, is a diagnostic marker in certain disorders.
A flattened or smooth philtrum, often accompanied by a thin upper lip and short palpebral fissures, is a characteristic facial feature of Fetal Alcohol Spectrum Disorders (FASD). These features are considered “sentinel” signs of prenatal alcohol exposure and are used in diagnosing Fetal Alcohol Syndrome (FAS) and partial FAS. Medical professionals use standardized tools, such as the University of Washington Lip-Philtrum Guides, to assess the philtrum’s smoothness and upper lip’s thinness, aiding accurate diagnosis. Their presence indicates alcohol exposure during a critical window of embryonic development, particularly around days 19-21 after conception, disrupted midline facial structure formation.