Facial symmetry is one specific measure of bodily symmetry. Along with traits such as averageness and youthfulness it influences judgments of aesthetic traits of physical attractiveness and beauty. For instance, in mate selection, people have been shown to have a preference for symmetry.Facial bilateral symmetry is typically defined as fluctuating asymmetry of the face comparing random differences in facial features of the two sides of the face. The human face also has systematic, directional asymmetry: on average, the face (mouth, nose and eyes) sits systematically to the left with respect to the axis through the ears, the so-called aurofacial asymmetry. Directional asymmetry
Directional asymmetry is a systematic asymmetry of some parts of the face across the population. A theory of directional asymmetries in the human body is the axial twist hypothesis. As predicted by this theory, the eyes, nose and mouth are, on average, located slightly to the left of the axis through the ears. This aurofacial asymmetry is very small in young adults (0.5 degree), but much larger in small children (4 degrees). Fluctuating asymmetry
Fluctuating asymmetry is the non-systematic variation of individual facial landmarks with respect to the facial midline, i.e., the line perpendicular to the line through the eyes, which crosses the tip of the nose and the chin. A wide variety of methods have been used to examine the claim that facial symmetry plays a role in judgments of beauty. Blending of multiple faces to create a composite and face-half mirroring have been among the techniques used.
Sexual selection can only influence features that potential mates can perceive, such as smell, audition (e.g. song) and vision. Such features might be reliable indicators of hidden fitness parameters such as a good immune system or developmental stability. It has been argued that more symmetric faces are preferred because symmetry might be a reliable sign of such hidden fitness parameters. However it is possible that high facial symmetry in an individual is not due to their superior genetics but due to a lack of exposure to stressors during development.It has been found that more symmetrical faces are rated as healthier than less symmetrical faces. Indeed, facial symmetry was found to be positively associated with the perceived healthiness of the facial skin. Also, facial asymmetry was found to be correlated with physiological, psychological and emotional distress.Some evidence suggests that face preferences in adults might be correlated to infections in childhood. See also
Beauty
Symmetry in nature
Patterns in nature
Physical attractiveness

References
External links
FaceResearch – Online studies on facial symmetry by researchers affiliated with University of Aberdeen (Scotland) School of Psychology, and University of St. Andrews (Scotland). "A facial symmetry plugin for the GIMP"—Try experimenting with facial symmetry, using open source software. "Psychological Image Collection at Stirling (PICS) Free Database of pictures of faces
"FaceBase An interdisciplinary research consortium for facial symmetry
"Tübinger Face Database An open research database of 200 merged 3-D faces
"A facial symmetry app for iPhone Experiment with facial symmetry, using a free iPhone app.