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PloS one2026; 21(1); e0337948; doi: 10.1371/journal.pone.0337948

Human emotional odours influence horses’ behaviour and physiology.

Abstract: Olfaction is the most widespread sensory modality animals use to communicate, yet much remains to be discovered about its role. While most studies focused on intraspecific interactions and reproduction, new evidence suggests chemosignals may influence interspecific interactions and emotional communication. This study explores this possibility, investigating the potential role of olfactory signals in human-horse interactions. Cotton pads carrying human odours from fear and joy contexts, or unused pads (control odour) were applied to 43 horses' nostrils during fear tests (suddenness and novelty tests) and human interaction tests (grooming and approach tests). Principal component analysis showed that overall, when exposed to fear-related human odours, horses exhibited significantly heightened fear responses and reduced interaction with humans compared to joy-related and control odours. More precisely, when exposed to fear-related odours, horses touched the human less in the human approach test (effect size: Rate Ratio(RR)=0.60 ± 0.24), gazed more at the novel object (RR = 1.32 ± 0.14), and were more startled (startle intensity - Cohen's d = -0.88 ± 0.39; and maximum heart rate - Cohen's d = 1.16 ± 0.47) by a sudden event. These results highlight the significance of chemosignals in interspecific interactions and provide insights into questions about the impact of domestication on emotional communication. Moreover, these findings have practical implications regarding the significance of handlers' emotional states and its transmission through odours during human-horse interactions.
Copyright: © 2026 Jardat et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Publication Date: 2026-01-14 PubMed ID: 41533708PubMed Central: PMC12803465DOI: 10.1371/journal.pone.0337948Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigates how human emotional odors, specifically fear and joy, influence the behavior and physiological responses of horses during various tests.
  • The research found that horses exposed to fear-related human odors showed increased fear behaviors and reduced positive interactions compared to those exposed to joy-related or control odors.

Introduction to the Research

  • Olfaction (sense of smell) is a critical sensory modality for animal communication.
  • Most previous research focused on how smell impacts communication within the same species (intraspecific) and reproductive behaviors.
  • New evidence suggests olfactory signals also play a role in communication across different species (interspecific), particularly related to emotions.
  • This study specifically explores how human emotional odors affect horse behavior, which is important for understanding human-animal interactions and domestication effects.

Methodology

  • Samples:
    • Cotton pads were used to collect human odors from contexts evoking fear and joy.
    • Unused cotton pads served as a control odor.
  • Participants: 43 horses.
  • Tests conducted:
    • Fear tests:
      • Suddenness test – measuring startle responses to unexpected events.
      • Novelty test – measuring reaction to new objects.
    • Human interaction tests:
      • Grooming test.
      • Approach test – measuring how horses physically interact with humans.
  • The cotton pads with the different odors were applied to the horses’ nostrils to ensure direct olfactory exposure.

Key Findings

  • Exposure to fear-related human odors caused significant behavioral and physiological changes in horses:
    • Horses exhibited heightened fear responses overall.
    • Decrease in positive interactions — notably, horses touched humans less during the approach test (Rate Ratio (RR) = 0.60 ± 0.24), meaning a 40% reduction compared to joy or control odors.
    • Increased attention and vigilance towards novel objects (RR = 1.32 ± 0.14), indicating more gaze time at unfamiliar stimuli.
    • Heightened startle responses to sudden events:
      • Greater startle intensity (Cohen’s d = -0.88 ± 0.39).
      • Increased maximum heart rate (Cohen’s d = 1.16 ± 0.47), suggesting elevated physiological arousal.
  • Joy-related and control odors did not provoke such fear-related responses, indicating specificity of the fear odor effect.
  • Principal component analysis was used to capture overall behavioral and physiological trends across the tests.

Implications and Significance

  • The research confirms that olfactory signals from humans can influence horses’ emotional states and behavior.
  • Highlights the importance of interspecific emotional communication mediated by smell, beyond just visual or auditory cues.
  • Provides insight into how domestication might have shaped emotional communication channels between humans and horses.
  • Practical relevance:
    • Handlers’ emotional states can be chemically transmitted to horses via odor, potentially affecting horse behavior and welfare.
    • Understanding these signals might improve safety and bond quality in human-horse interactions by managing handler emotions.

Concluding Remarks

  • This study demonstrates a clear link between human emotional odors and changes in horse behavior and physiological responses during fear and human interaction scenarios.
  • It broadens our understanding of how animals interpret human emotional cues through olfaction, an often-overlooked sensory modality in human-animal communication research.
  • Future research may explore how these findings extend to other domesticated animals and different human emotional states.

Cite This Article

APA
Jardat P, Destrez A, Damon F, Tanguy-Guillo N, Lainé AL, Parias C, Reigner F, Ferreira VHB, Calandreau L, Lansade L. (2026). Human emotional odours influence horses’ behaviour and physiology. PLoS One, 21(1), e0337948. https://doi.org/10.1371/journal.pone.0337948

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 21
Issue: 1
Pages: e0337948
PII: e0337948

Researcher Affiliations

Jardat, Plotine
  • Institut Français du Cheval et de l'Equitation, Pôle développement, Innovation et Recherche, Nouzilly, France.
  • INRAE, CNRS, Université de Tours, PRC, Nouzilly, France.
Destrez, Alexandra
  • Development of Olfactory Communication and Cognition Laboratory, Centre des Sciences du GoÛt et de l'Alimentation, Institut Agro Dijon, CNRS, Université de Bourgogne-Franche-Comté, Inrae, Dijon, France.
Damon, Fabrice
  • Development of Olfactory Communication and Cognition Laboratory, Centre des Sciences du GoÛt et de l'Alimentation, Institut Agro Dijon, CNRS, Université de Bourgogne-Franche-Comté, Inrae, Dijon, France.
Tanguy-Guillo, Noa
  • INRAE, CNRS, Université de Tours, PRC, Nouzilly, France.
Lainé, Anne-Lyse
  • INRAE, CNRS, Université de Tours, PRC, Nouzilly, France.
Parias, Céline
  • INRAE, CNRS, Université de Tours, PRC, Nouzilly, France.
Reigner, Fabrice
  • UEPAO, INRAE, Nouzilly, France.
Ferreira, Vitor H B
  • INRAE, CNRS, Université de Tours, PRC, Nouzilly, France.
Calandreau, Ludovic
  • INRAE, CNRS, Université de Tours, PRC, Nouzilly, France.
Lansade, Léa
  • INRAE, CNRS, Université de Tours, PRC, Nouzilly, France.

MeSH Terms

  • Horses / physiology
  • Animals
  • Humans
  • Behavior, Animal / physiology
  • Emotions / physiology
  • Fear / physiology
  • Odorants
  • Male
  • Female
  • Smell / physiology

Conflict of Interest Statement

The authors declare no competing interests.

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