Smooth philtrum
Page most recently updated 7 September 2026
This page focuses on smooth philtrum as a morphologic feature of conditions that may also be associated with psychiatric manifestations, such as psychosis, mania, autism spectrum disorder, ADHD, OCD, and self-injurious behaviours. The page begins with a clinical definition of smooth philtrum based on the standardized Elements of Morphology terminology, together with visual examples from the same source. This is followed by a list of conditions in which smooth philtrum has been described in association with psychiatric manifestations.
Of note, to optimize clinical utility, the list does not include conditions associated with intellectual disability in the absence of other psychiatric features.
Each condition listed below is linked to a dedicated page within this resource. These pages describe the psychiatric manifestations associated with each condition, as well as other morphologic and broader clinical features, allowing the differential diagnosis to be considered from multiple perspectives.
Smooth philtrum
The patient in the upper panel has a smooth philtrum. The lower two panels show a patient with a normal philtrum, demonstrating how facial movement can create the false impression of a smooth philtrum, as seen in the lower panel.
The University of Washington Lip-Philtrum Guides ➚ provide pictorial standards for assessing philtrum smoothness and upper-lip thinness.
Image credit: National Human Genome Research Institute (NHGRI), Elements of Morphology.
Definition
Subjective: Flat skin surface, with no ridge formation in the central region of the upper lip between the nasal base and upper vermilion border.
Note: There is a spectrum of this finding from total absence of the philtral ridges to some prominence of the ridges. The central groove varies from absent to shallow. Grading of the smoothness of the philtrum, used in the assessment of Fetal Alcohol Syndrome (Astley and Clarren, 1995) (University of Washington Lip-Philtrum Guides ➚), has been developed. This finding is greatly influenced by the facial expression, and care should be taken to evaluate the philtrum when the face is in a neutral position. A smooth philtrum can be associated with a long philtrum. However, the two findings should be considered separately.
Synonyms: Flat philtrum.
Replaces: Indistinct philtrum; Simple philtrum.
Selected references and further reading — Morphologic lens
Allanson JE, Biesecker LG, Carey JC, Hennekam RCM. Elements of morphology: introduction. Am J Med Genet A. 2009;149A(1):2-5.
Hennekam RCM, Biesecker LG, Allanson JE, Hall JG, Opitz JM, Temple IK, Carey JC; Elements of Morphology Consortium. Elements of morphology: general terms for congenital anomalies. Am J Med Genet A. 2013;161A(11):2726-2733.
Jones KL, Jones MC, del Campo M. Smith's recognizable patterns of human malformation. 8th ed. Philadelphia: Elsevier; 2021.
Reardon W. The bedside dysmorphologist: a guide to identifying and assessing congenital malformations. 2nd ed. Oxford: Oxford University Press; 2016.