Botulinum Toxin and Social Perception: Effects of Upper-Face Treatment on Facial Emotion Attribution

Upper-face botulinum toxin type A (BoNT-A) treatments are capable of reducing muscular activity in the glabella, forehead, and lateral canthal region, which play pivotal roles for core emotional expressions. Although concerns about reduced expressivity are common, little is known about how observers perceive emotional expressions in individuals following upper-face BoNT-A.

To examine whether upper-face BoNT-A treatments alter observers' emotion attribution and perceived emotion intensity of facial expressions, while examining whether any emotion-specific changes occur in alignment with the treated musculature.

A total of 118 raters (71 female, 47 male; mean age 37.0 ± 11.6 years) evaluated standardized images of BoNT-A-treated individuals posing four emotional expressions (anger, joy, surprise, neutral) at three time points: pre-treatment (V1), peak effect at 2 weeks (V2), and follow-up at 16 weeks (V3). Motion in the glabellar, frontalis, and lateral canthal regions was quantified using 3D surface scans to assess treatment-related changes in facial movement. Raters identified the posed emotion and rated its perceived intensity.

Upper-face BoNT-A produced the expected reduction in upper-face muscle movement at peak effect with partial recovery at follow-up. Emotion attribution showed small overall changes but pronounced emotion-specific differences: attribution of anger and surprise decreased substantially from baseline to peak effect, whereas attribution of joy and neutral expressions remained stable. Perceived intensity showed a similar but less pronounced pattern.

Upper-face BoNT-A leads to a temporary, anatomically aligned, and emotion-specific attenuation of anger and surprise attribution while preserving pleasant and neutral emotional signaling. Importantly, no evidence of a global "frozen face" appearance emerged. These findings emphasize the importance of integrating facial emotional expression into pre-treatment assessment and using precise, region-specific neuromodulation to align aesthetic outcomes with individual patient intentions.