Development of a proposed guide to identify, screen and appraise self-report and device-based measures of habitual physical activity in systematic reviews: a methodological protocol.

Olfaction, often considered the most ancient and visceral of the senses, plays a profound role in human social life. The olfactory system has direct neural pathways to brain regions central to emotion and memory, such as the amygdala and the hippocampus (; ). This unique neuroanatomy positions smell as a potent channel for chemosignals, potentially influencing our judgments, emotions and social behaviors often outside of conscious awareness (). Importantly, this privileged access to limbic circuitry suggests that olfactory inputs may shape social evaluation at both automatic and inferential levels. In recent decades, a growing body of research has begun to systematically investigate how odors serve as invisible social stimuli. The conceptual framework often draws from the concept of the “Behavioral Immune System” (BIS) (), which proposes that humans have evolved psychological mechanisms to detect and avoid pathogens. As body odors can be cues to disease, this system may manifest in social contexts as prejudice or avoidance of out-groups perceived to have different hygiene practices (; ). Within this framework, disgust emerges as a central affective mechanism linking sensory input to social evaluation. Notably, converging evidence suggests that disgust operates as a transdiagnostic construct across clinical conditions () and plays a broader role in shaping both affective and social processing (, ).