«Symmetry 2010, 2, 1925-1944; doi:10.3390/sym2041925 OPEN ACCESS symmetry ISSN 2073-8994 Article Three-Dimensional ...»
Symmetry 2010, 2, 1925-1944; doi:10.3390/sym2041925
Three-Dimensional Facial Asymmetry in Attractive and Normal
People from Childhood to Young Adulthood
Chiarella Sforza 1,*, Alberto Laino 2, Gaia Grandi 1, Luca Pisoni 1 and Virgilio Ferruccio Ferrario 1
Laboratorio di Anatomia Funzionale dell’Apparato Stomatognatico, Dipartimento di Morfologia
Umana e Scienze Biomediche “Città Studi”, Università degli Studi di Milano, 20122 Milan, Italy;
E-Mails: Gaia.Grandi@gmail.com (G.G.); Luca.Pisoni@studenti.unimi.it (L.P.);
Virgilio.Ferrario@unimi.it (V.F.F.) Dental, Oral, and Maxillo-Facial Sciences, Section of Orthodontics, University Federico II, 80125 Naples, Italy; E-Mail: Alberto.Laino@unina.it * Author to whom correspondence should be addressed; E-Mail: Chiarella.Sforza@unimi.it.
Received: 1 October 2010 / Accepted: 19 October 2010 / Published: 9 November 2010 Abstract: We are currently investigating measurable esthetic characteristics in persons considered “attractive” by the media. Three-dimensional soft-tissue facial asymmetry was quantified in 380 attractive (148 males, 232 females) and 669 control (397 males, 272 females) healthy persons aged 4–30 years. The coordinates of 50 facial landmarks were collected by a computerized digitizer, and asymmetry computed. Soft-tissue facial asymmetries reduced as a function of age in all cases. Attractive children were more symmetric than control children, but the reverse was true for young adults. The effect of symmetry on attractiveness seems to change as a function of age.
Keywords: attractiveness; face; symmetry; three-dimensional
1. Introduction Asymmetry is a common finding in both the craniofacial hard tissues, and in the facial appearance, where the soft tissue cover (muscles, skin, adipose tissue) may partly mask the underlying imbalances [1–9]. Asymmetry is also found in the movement of facial mimic muscles: in healthy subjects, facial expressions, and in particular spontaneous smile, are larger on the left- than on the right-side of the face [10–12].
Symmetry 2010, 2 1926 Facial asymmetry is better appreciated using a three-dimensional approach that allows a direct measurement of the two facial halves [6,7,13,14], because the visual, qualitative assessment is often insufficient. For instance, skeletal asymmetries of less than 3% are not clinically discernible [5,15]. If the points of ear insertion cannot be easily identified, facial depth may be of difficult visual evaluation . Indeed, in the face all three spatial components (right-left, cranio-caudal, anteriorposterior) can be asymmetric. In particular, the facial lower third can be very asymmetric in the anteroposterior plane [2,8], a finding neglected in the conventional two-dimensional photographic or radiographic views [1,5,17–19].
According to the current theories of evolutionary psychology, the esthetic assessment of adult faces depends on various combinations of averageness, symmetry, neoteny (babyness) and youthfulness, and sexual dimorphism [19–27]. Additionally, facial expression (happiness, excitement, arousal) and grooming (successful adaptation, status) concur to a global positive assessment .
Both natural and sexual selections seem to explain the various perceptions of attractiveness, with almost consistent ratings across sexes, ethnic groups and ages [13,20,24–26]. Recently, these investigations were extended also to children and adolescents [28–31]. Overall, the studies confirmed some of these theories: attractive children, female adolescents and adult women had faces with several characteristics of babyness: a large face with a relatively large forehead; relatively prominent cheekbones; reduced vertical development; full and prominent lips, and a more convex soft-tissue facial profile, than normal coetaneous persons [20,21,28–32]. In contrast, in post-pubertal adolescent boys and adult men, attractiveness seems to be positively influenced by facial markers of high testosterone levels (a signal of sexual dimorphism), with a relative increment of the facial lower third (more prominent chin, less prominent lips) [20,22,25,30,33].
In our laboratory, we are currently studying the three-dimensional facial characteristics of children, adolescents, adult males and females considered “attractive” by the general public [30–32]. Their facial soft tissues were measured with a non-invasive computerized instrument, several measurements obtained, and compared to those collected in healthy persons of the same sex, age and ethnicity, selected using criteria of dentofacial normality (Figure 1). The presence of measurable specific characteristics was assessed. If esthetically pleasing faces possess some kind of codified facial dimensions, angles and ratios, these measurements could be used by medical and dental practitioners for a better patient care [6,9,34]. Previous investigations performed on these attractive persons assessed the hypotheses of babyness/ youthfulness (found to explain a large part of facial attractiveness in children, adolescent girls, and adult women) and of sexual dimorphism (an effect found in adult women, in male adolescents, and in adult men) [30–32]. On no occasion, was data about their facial symmetry/ asymmetry assessed.
Symmetry 2010, 2 1927 Figure 1. Facial landmarks digitized on all subjects for subsequent morphometric calculations. Midline landmarks: tr, trichion; g, glabella; n, nasion; prn, pronasale;
c’, columella; sn, subnasale; ls, labiale superius; sto, stomion; li, labiale inferius;
sl, sublabiale; pg, pogonion; me, menton. Paired (right and left side) landmarks:
ex, exocanthion; en, endocanthion; os, orbitale superius; or, orbitale; ft, frontotemporale;
chk, cheek; zy, zygion; t, tragion; al, alare; ac, nasal alar crest; itn, inferior point of the nostril axis; stn, superior point of the nostril axis; cph, crista philtri; ch, cheilion; go, gonion; pra, preaurale; sa, superaurale; pa, postaurale; sba, subaurale.
1.1. Facial Symmetry and Attractiveness
Asymmetry can be divided into antisymmetry, directional and fluctuating asymmetry. In antisymmetry, either side of the body could be dominant (for instance, handedness). Directional asymmetry is consistently dominant on one side (for instant, heart position), while fluctuating asymmetry relates to traits that are on average symmetric in a population. Fluctuating asymmetry is considered to result from unbalances in growth and development of the various structures, with a reduced capacity of the organism to buffer environmental disturbances and genetic stressors [4,13,14,19,26,35–37]. From this point of view, the assessment of fluctuating asymmetry may provide useful information about the combined action of developmental stress and individual capacity to react.
An increased fluctuating asymmetry has been related to higher morbidity and mortality, reduced fecundity, inferior locomotory performance [13,35]. In contrast, a reduced fluctuating asymmetry has been associated with increased attractiveness, both in the face and in the body [13,19,21–24,27].
Symmetry 2010, 2 1928 Current explanations about the effect of facial symmetry on attractiveness can be summarized into three main aspects: symmetry is an important signal of good health and developmental stability; during visual inspection, symmetric faces are easier to scan and understand; symmetric faces are nearer to the average, prototype face [19,21–24,27]. Persons with symmetric faces and bodies suggest to the observer that they possess good genes, a good general health, and are more resistant to diseases and parasites. Symmetric faces become “honest” markers of genotype and phenotype quality: Symmetry reflects the individual ability to maintain a stable development notwithstanding the environmental stress, thus being the result of natural selection [4,13,19,21,23,24,26,36,38].
Despite these theories, not all investigators concord about a strict relationships between facial symmetry and attractiveness from one side, and facial asymmetry and disease (or altered development) from the other side [1,12,18,21,27,36,38]. For instance, Peck et al.  found that men and women considered attractive by the general public (beauty competition winners, professional models) had asymmetries in one or more craniofacial skeletal dimensions. Zaidel and Hessamian  found that both full and hemi-faces (only right or left side of the face) were rated similarly in terms of attractiveness. Shaner et al.  did not find an increase in soft-tissue facial asymmetry in syndrome affected individuals as compared to normal persons.
In our previous investigations, among the various analyzed parameters, the effect of facial symmetry on attractiveness was not considered. In the current study, we assessed the effect of facial symmetry/asymmetry on attractiveness by analyzing a wide group of attractive persons of both sexes ranging from four to 30 years of age, as well as a group of normal persons of the same age, sex and ethnic group. Their fluctuating soft-tissue facial asymmetry was quantitatively obtained from the three-dimensional coordinates of selected soft-tissue facial landmarks . In a first analysis, linear distances and landmark coordinates were considered using a method previously developed in our laboratory, and that had been used to assess sex- and age- related variations in healthy people, as well as the effect of pathology and relevant treatment [3,8,39]. The method has been constructed considering the object symmetry of the human face ; it allows to separate the effect of selected landmarks to the total facial asymmetry, as recently underlined , and it has proved to supply clinically relevant information [8,39].
Attractive persons were selected by casting agencies or by judges of beauty competitions, without any knowledge of the aims and scope of the current investigations (see details below). Similar protocols were followed by Peck et al.  and by Ing et al.  for two-dimensional hard- and softtissue craniofacial characteristics. This procedure contrasts with that followed in most studies about facial attractiveness, where the judgment was made on photographs (both original images, and composite or manipulated faces) of unselected persons [19,21–26,33,36,38].
1.2. Selection of Attractive Persons
several national beauty competitions, which took place in Italy between 2006 and 2008. They were those admitted to the semi-final and final stages of beauty competitions, and were measured just before the semi-final stage of the relevant competition .
2. Results and Discussion
2.1. Total, Midline and Lateral Facial Asymmetry In both sexes, attractive and control subjects significantly differed in several of the analyzed symmetry descriptors, which assessed separately the contribution of the midplane (DFSm) and lateral (DFSl) asymmetries to the total facial asymmetry (DFSt) (Table 1). In both sexes, the factor age (two-way factorial analysis of variance) was always significant (p 0.001), with a general trend of reduced asymmetry with growth and development (Figures 2–4). Similar patterns were obtained by both the lateral symmetry and the midline symmetry. Indeed, as suggested by Klingenberg et al. , the analysis of object symmetry (a structure symmetric in itself, because it is intersected by the midsagittal plane) should consider the variations of structural features in the median plane separately from those of the features located in the right and left sides.
According to Haraguchi et al. , the level of two-dimensional soft-tissue facial asymmetry was independent from age or sex of the subject. Similar results were reported by Rossi et al.  for threedimensional skeletal measurements. In contrast, in healthy subjects Ferrario et al.  reported that three-dimensional soft-tissue facial asymmetry decreased from adolescence to adult age, a finding well replicated in the current study for both control and attractive subjects (Figures 2–4). It appears that the level of asymmetry, and its distribution in the population, depends on both the analyzed structures (hard vs. soft tissues), and the used method (two- vs. three-dimensional assessment).
In control male subjects, lateral asymmetry was always larger than midplane symmetry, contributing between 71% (4–5 year-old boys and 15–17 year-old adolescents) and 91% (8–10 year-old boys) to the total facial asymmetry. In attractive boys and men, a different pattern was observed, with lateral asymmetry explaining only up to 68% (4–5 year-old boys) of total asymmetry.
Similar patterns of lateral/ midplane asymmetry contributions were observed in control (between 46 and 96%) and attractive (between 49 and 61%) females. For control subjects, these values were Symmetry 2010, 2 1930 somewhat lower than those previously reported by Ferrario et al.  for healthy adolescents and young adults.
Percentage asymmetry was assessed to account for the different facial dimensions in the analyzed age groups and in the two sexes. In the youngest girls, percentage asymmetry was on average 20–25% of the nasion–facial barycenter distance, and it reduced to 15% in the subsequent age groups (Figure 4). In adolescent girls and in adult women, it remained lower than 12%, except in attractive women (“Miss”), with an average percentage asymmetry of about 15%. For control “old” adolescent girls and women, these values were very similar to those previously reported in literature .
Symmetry 2010, 2 1931
Similar values were found in boys: the average percentage asymmetry was between 20 and 25% in the youngest age group, with subsequent reductions of around 15%. Adolescent and adult males had average percentage asymmetry values very close to those found in females (around 12%); the largest value was found in the attractive men (“Mister”). Literature reports for adolescent boys aged 12 to 15 years (comparable with the current “young” adolescent boys) and for young adult men are in good accord with the current values .