A Psychological Guide to Lower Face Botulinum Toxin Injections: Baseline Emotional Functions of Facial Expressions

The lower face conveys critical interpersonal signals and is central to how patients are emotionally evaluated by others. As botulinum toxin type A (BoNT-A) is increasingly used in the perioral and mandibular region, there is a growing need to understand how such procedures may influence both aesthetic outcomes and the dynamics of emotional communication and social perception.

This narrative review outlines the baseline emotional functions of lower-face expressions and supports clinicians in integrating emotional and interpersonal considerations into BoNT-A treatment planning.

A narrative literature review was conducted using PubMed and Scopus, combining the search terms 'botulinum toxin', 'lower face', 'facial expression', 'emotion', 'mimicry', and 'psychology'. Relevant evidence from psychology and neuroscience was synthesized to identify emotional and social signaling functions of key lower-face Action Units (AUs). Additional insights were integrated through citation tracking and clinical experience.

Lower-face BoNT-A targets, such as the depressor anguli oris, platysma, masseter, mentalis, and orbicularis oris, are part of distinct AUs that contribute to emotion expression and interpersonal signaling. Their modulation through BoNT-A potentially alters cues linked to socially relevant emotions such as sadness and contempt, and social dimensions, including dominance and approachability, thereby affecting how patients are perceived in social contexts.

Understanding the psychological and communicative functions of the lower face helps anticipate how BoNT-A treatments may influence emotional signaling and social perception. Incorporating these insights into aesthetic consultations supports transparent counseling and strengthens awareness of how aesthetic interventions contribute to nonverbal communication.