How Sex Shapes Facial Morphology in Adults: A 3D Geometric Morphometric Study

Background/Objectives: An accurate description of facial sexual dimorphism is essential in clinical, forensic, and anthropological contexts to support accurate diagnosis of craniofacial dysmorphisms and differences, treatment planning and evaluation, as well as biological profiling, craniofacial reconstruction, and personal identification. This study investigates sexual dimorphism of the facial soft tissues in a sample of healthy Italian adults, providing reference data and deepening our understanding of normal craniofacial variation. Methods: Three-dimensional stereophotogrammetric facial images of 342 Italian adults (172 males and 170 females; 18-40 years old) were analyzed using a 3D spatially dense geometric morphometric approach to assess both shape and form. Principal Component Analysis (PCA) and Partial Least Squares Regression (PLSR) were used to explore facial variation and to quantify sex-related differences. Results: Centroid size was significantly larger in males. While PCA revealed that sex is a significant factor in facial shape and form variation, PLSR highlighted the existence of significant associations between sex and both shape and form. Color-coded morphometric maps underlined the most sexually dimorphic traits: males exhibited bigger faces with deep-set eyes and central facial projection extending from the supraorbital rims to the chin, whereas females display smaller faces with fuller cheeks, and a more vertical forehead profile. Conclusions: While our results are consistent with those of previous studies, our study revealed important, distinctive group-specific traits: flatter labiomandibular folds in males and wider temples and fuller cheeks in the infraorbital region extending to zygomatic and mandibular areas in females. Thus, this study provides high-resolution reference data supporting related applications.