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 is systematic. The average across the population is not "symmetric", but statistically significantly biased on one direction. That means, that individuals of a species can be symmetric, or even asymmetric to the opposite side (see, e.g., handedness), but most individuals are asymmetric to the same side. The relation between directional and fluctuating asymmetry is comparable to the concepts of accuracy and precision in empirical measurements.

There are examples from the brain (Yakovlevian torque) and spine, and inner organs (see axial twist theory), but also from various animals (see Symmetry in biology).

Aurofacial asymmetry (from Latin auris 'ear' and facies 'face') is an example of directed asymmetry of the face. It refers to the left-sided offset of the face (i.e. eyes, nose, and mouth) with respect to the ears. On average, the face's offset is slightly to the left, meaning that the right side of the face appears larger than the left side. The offset is larger in newborns and reduces gradually during growth.

In contrast to fluctuating asymmetry, directional asymmetry is systematic, i.e. across the population it is systematically more often in one direction than in the other. It means that across the population a deviation is more often to one direction than to the other, i.e., there is a statistically significant bias to one direction. In case of directional asymmetry, most individuals of a species are asymmetric to the same side, even though some individuals can be symmetric, or even asymmetric to the opposite side (cf., e.g., handedness). The relation between directional and fluctuating asymmetry is comparable to the concepts of accuracy and precision in empirical measurements.

The aurofacial asymmetry is defined as the position of the face (mouth, nose and eyes) with respect to the mid plane of the axis through the ears. The asymmetry is expressed as an angle (degrees), i.e. by how many degrees facial landmarks (e.g. tip of the nose) or pairs of landmarks (e.g. inner corners of the eyes (endocanthions are rotated away from the mid plane between the ears.

On average, the aurofacial asymmetry is slightly larger for the eyes than for the nose, as shown by the figure.