Abstract: This review synthesizes recent empirical findings on emotional body odors (EBOs) and advances a unified evolutionary framework that repositions EBOs as adaptive chemical communicators rather than unanalyzed background cues. Rather than repeat basic definitions, the review focuses on three innovations. First, it integrates multi-level evidence—behavioral, autonomic, electrophysiological, neuroimaging, and molecular—to map the specific response profiles that different EBOs evoke in receivers. Second, it offers a critical molecular and receptor-level appraisal that challenges the default classification of EBOs as pheromones. Third, it proposes the “communicative chemical evolution hypothesis,” a testable model that links learning, selection, and population dynamics to stages in the functional maturation of chemical signals.
Empirical synthesis reveals reproducible, emotion-specific effects. Negative EBOs (fear, anxiety, anger, sadness) trigger rapid threat-oriented cascades. Fear body odor (FBO) reliably increases sympathetic markers, modulates facial motor responses (orbicularis oculi, corrugator supercilii), reduces heart rate variability, and biases perceptual and decision processes toward threat. Electrophysiology shows early sensory amplification (N1/P1) and enhanced face-processing components (N170, P3), while neuroimaging highlights amygdala-fusiform-ventromedial prefrontal circuits that mediate threat detection and attention allocation. Anxiety odors produce similar autonomic shifts, strengthen startle reflexes, and bias risk assessment. Anger odors amplify skin conductance and recruit thalamic-hypothalamic-insula-amygdala-cingulate pathways, particularly in high-trait-anxiety participants. Sadness-related chemosignals (e.g., from tears) decrease testosterone and sexual arousal in males, and dampen hypothalamic and reward-related responses. By contrast, positive EBOs (e.g., happiness odor) increase parasympathetic indices, induce Duchenne smiles, elevate late positive potentials (LPP), and enhance cognitive flexibility and cooperative tendencies. Across studies, the functional dichotomy is robust: negatives favor rapid defense and avoidance; positives promote affiliation and exploration.
Comparative and cross-cultural evidence provides preliminary support for partial universality. Cross-species responses to FBOs (dogs, horses) and consistent effects across East Asian and Western samples suggest conserved processing biases. However, most evidence stems from controlled lab paradigms that use direct nasal delivery of concentrated samples. This raises ecological validity concerns and limits inferences about real-world sender-receiver dynamics.
At the molecular level, the review identifies a central gap: EBOs lack clearly identified, steroidal molecules at biologically plausible concentrations that would parallel classical pheromones (e.g., androstadienone). Receptor evidence is likewise scarce, and human vomeronasal function appears vestigial. These facts argue against uncritical classification of EBOs as pheromones. The review proposes instead that EBOs function primarily via the main olfactory epithelium and associative learning mechanisms, interacting with individual experience to produce stable behavioral regularities.
The communicative chemical evolution hypothesis formalizes this view. It frames EBOs on a continuum from chemical cues (metabolic by-products) to chemical signals (contextually exploited cues) and, under stringent conditions of genetic fixation and sender-receiver reciprocity, to releaser pheromones. The model emphasizes three drivers of functional transition: (1) unique chemical features that allow consistent discrimination; (2) repeated cue-response pairings that generate learned associations and canalize responses; and (3) population-level selection that stabilizes sender and receiver strategies (a Baldwin-effect mechanism). By integrating learning and selection, the model explains cross-cultural consistency without presuming purely innate coding.
The review also evaluates empirical limitations and methodological fixes. Current work over-relies on single-receiver paradigms, neglects sender benefits, and ignores chronic exposure consequences. To move the field forward, the review recommends: multi-agent interaction experiments to capture bidirectional dynamics; twin and family designs to partition genetic and experiential variance; longitudinal intergenerational sampling to detect fixation; virtual reality coupled with high-resolution olfactometers for ecological control; and metabolomic fingerprinting to discover candidate biomarkers. These approaches will enable direct tests of sender-receiver reciprocity, fitness consequences, and the molecular prerequisites for pheromone status.
Finally, the review sketches translational pathways. If validated, EBO-based interventions could augment exposure therapies, enhance social-skill training, or serve as adjuncts in assistive technologies for autism spectrum disorders. Yet translation requires caution: weak effect sizes, contextual dependence, and ethical issues around manipulation of chemosignals demand rigorous validation.
In sum, this review advances theory and method by (1) distinguishing signal from cue at molecular and behavioral scales, (2) articulating a testable evolutionary pathway for EBOs, and (3) specifying concrete empirical programs to evaluate whether, when, and how human emotional chemosignals become evolutionarily stabilized communicative tools.

Key words: emotional body odor, emotional communication, olfaction, pheromones, chemical communication