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Breath: The Major Source of Odors in Hunting or Wildlife Observation

The Hunter's Scent Signature: Why Breath is Your Greatest Threat

When hunting, understanding and controlling body odour has always been an absolute priority1. This article explains why breath can account for over 80% of your scent signature and how it is influenced by various factors. It is crucial to note that this analysis focuses on odours dynamically emitted by the body and does not take into account external contamination from clothing and equipment. Once properly decontaminated, these items do not release significant odours.

Breath: A Far More Significant Source of Odours Than Skin

Most hunters believe that sweat and skin are the main sources of odours, while scientific studies clearly demonstrate that breath is the dominant source. In certain conditions, exhaled air can account for up to 80% or more of the volatile organic compounds (VOCs) that betray a hunter's presence, as these odours are released and projected into the environment.

The Link Between Blood and Breath

To understand this phenomenon, you must first know that the air we exhale is not just spent oxygen. It is in direct contact with our blood in the lungs. The blood, which circulates constantly throughout the body, transports waste and compounds produced by our metabolism2. With each heartbeat, these volatile molecules pass from the blood capillaries into the air in our lung alveoli, and are then naturally expelled with each exhalation. This process is constant and unavoidable, turning every breath into a unique "chemical fingerprint."

Number of Identified Organic Compounds

Recent studies have identified a total of 1849 different volatile organic compounds originating from the human body. Breath is by far the richest source, containing the greatest variety of these compounds.


The graph below illustrates the distribution of the number of these compounds by bodily source3,4.

Amount of VOCs Released at Rest

For a hunter, the main sources of odours are breath and skin. A healthy adult person at rest releases a total of 2440 µg/h of VOCs from these two sources. As the following graph shows, respiration's contribution is already the majority. This is only part of the story. Clothing, wind, physical exertion, and diet radically change these proportions.

The Clothing Barrier Effect

When hunting, we wear several layers of clothing. The VOCs emitted by the skin are absorbed and retained by these textiles, which act as true sponges. This is why our clothes smell after being worn and need to be washed: they have accumulated body odours. Mass spectrometry-chromatography studies show that textiles can retain up to 80% of VOCs5,6. However, this research has focused on a single layer of clothing worn directly on the skin, a factor that is not considered for hunting gear, which often involves wearing multiple layers to optimize insulation and trap odours more effectively. Thus, clothing significantly limits the release of these odours into the environment. For this reason, even when lightly dressed, breath remains the major source of our scent signature.

  • Breath: 1,290 µg/h, or about 85% of released VOCs.
  • Skin (residual release): 230 µg/h, or about 15% of released VOCs (after 80% retention by clothing).

Wind: A Vector that Amplifies Your Scent Signature

Unlike skin odours, which are largely retained by clothing, your breath acts as a constant odour projector. Each breath is a jet of warm air, rich in hundreds of volatile molecules, expelled directly into the environment7. This is where wind comes in. Instead of dissipating, this plume of air is immediately captured and transported over long distances. Imagine a cloud of smoke projected by a locomotive: this cloud does not disappear; it is actively moved and stretches into a long trail3. This is exactly what happens to your breath, creating a genuine "scent trail" that game can detect long before they see you. In a scenario with even a light breeze, it is breath that becomes the most formidable source of odour. The wind projects these powerful odours so far and so effectively that the skin's contribution to your scent signature becomes largely eclipsed. This is why managing your breath is the absolute priority, much more so than your skin.

 

In summary, if your clothes are an effective barrier for your body odour, it is the wind that turns your breath into your greatest threat.

Other Factors Influencing the Breath Scent Signature

The profile of exhaled VOCs varies greatly from person to person and is affected by many internal and external factors.


Metabolism and Physical Activity

  • Basal Metabolism: An active person or an athlete will have a higher basal metabolism, which increases the production of VOCs, such as acetone, a marker of fat burning. Conversely, a sedentary person will naturally produce less8,9.
  • Prolonged Exercise: Walking or intense physical activity (like tracking) forces the body to tap into its fat reserves, increasing acetone production. Studies show an increase in exhaled acetone of up to +25% in people exercising8,10,11,12. A hunter out of breath after a long walk will therefore be more odorous than when at rest.


Health and Diet

  • General Health: Metabolic diseases like diabetes13 can profoundly modify the VOC profile. Poorly controlled diabetes can cause acetone concentration to climb from a few ppm to several dozen14.
  • Diet: Fasting, even intermittent, can increase exhaled acetone by about 35%11. Furthermore, gut microbiota ferment nutrients into volatile fatty acids that can be exhaled15.


Individual Variations and Other Factors

  • Age, sex, genetics, smoking, medication use, and hydration are also factors that modify exhaled VOCs16,17. These variations explain why each individual has a unique scent signature and why two hunters can emit very different odours under similar conditions.

Animal Olfactory Detection

The importance of these VOCs is multiplied when we know that deer and dogs have an extraordinarily powerful sense of smell. A dog can detect odours at concentrations 100,000 times lower than humans. They are even capable of smelling and detecting metabolic disorders and cancers1,18.

 

In conclusion, while controlling skin odours is essential, it is equally crucial to understand that breath is a continuous and powerful source of odours, influenced by many factors19.
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References

  1. McCoy, C. (n.d.). The Science Behind a Deer's Sense of Smell & Scent Control. North American Whitetail. Consulté le 18 août 2025, sur https://www.northamericanwhitetail.com/editorial/science-behind-deers-sense-of-smell-scent-control/368596
  2. Chou, H., Godbeer, L., Allsworth, M., Boyle, B., & Ball, M. L. (2024). Progress and challenges of developing volatile metabolites from exhaled breath as a biomarker platform. Metabolomics, 20(1), Article 72. https://doi.org/10.1007/s11306-024-02142-x
  3. Wang, N., Ernle, L., Bekö, G., Wargocki, P., & Williams, J. (2022). Emission rates of volatile organic compounds from humans. Environmental Science & Technology, 56(8), 4838–4848. https://doi.org/10.1021/acs.est.1c08764
  4. Amann, A., de Lacy Costello, B., Miekisch, W., Schubert, J., Buszewski, B., Pleil, J., Ratcliffe, N., & Risby, T. (2014). The human volatilome: Volatile organic compounds (VOCs) in exhaled breath, skin emanations, urine, feces and saliva. Journal of Breath Research, 8(3), Article 034001. https://doi.org/10.1088/1752-7155/8/3/034001
  5. Soares, T. A., Owsienko, D., Haertl, T., & Loos, H. M. (2023). Recovery rates of selected body odor substances in different textiles applying various work-up and storage conditions measured by gas chromatography–mass spectrometry. Journal of Chromatography A, 1685, Article 463680.
  6. Chou, H., Godbeer, L., Allsworth, M., Boyle, B., & Ball, M. L. (2024). Progress and challenges of developing volatile metabolites from exhaled breath as a biomarker platform. Metabolomics, 20(1), Article 72. https://doi.org/10.1007/s11306-024-02142-xhttps://doi.org/10.1177/0040517520914411
  7. Celani, A., Villermaux, E., & Vergassola, M. (2014). Odor landscapes in turbulent environments. Physical Review X, 4(4), Article 041015. https://doi.org/10.1103/PhysRevX.4.041015
  8. Heaney, L. M., & Lindley, M. R. (2018). Translation of exhaled breath volatile analyses to sport and exercise applications. European Journal of Sport Science, 18(4), 461–470.
  9. Heaney, L. M., Kang, S., Turner, M. A., Lindley, M. R., & Thomas, C. L. P. (2019). The impact of a graded maximal exercise protocol on exhaled volatile organic compounds: A pilot study. Journal of Breath Research, 13(3), Article 036001.
  10. Henderson, B., Batista, G. L., Bertinetto, C. G., Meurs, J., Materić, D., Bongers, C. C. W. G., Allard, N. A. E., Eijsvogels, T. M. H., Holzinger, R., Harren, F. J. M., Jansen, J. J., Hopman, M. T. E., & Cristescu, S. M. (2021). Exhaled breath reflects prolonged exercise and statin use during a field campaign. Metabolites, 11(4), Article 192. https://doi.org/10.3390/metabo11040192
  11. Bastide, G. M. G. B. H., Remund, A. L., Oosthuizen, D. N., Derron, N., Gerber, P. A., & Weber, I. C. (2023). Handheld device quantifies breath acetone for real-life metabolic health monitoring. Sensors & Diagnostics, 2(4), 918–928. https://doi.org/10.1039/D3SD00079F
  12. Bovey, F., Cros, J., Tuzson, B., Seyssel, K., Schneiter, P., Emmenegger, L., & Tappy, L. (2018). Breath acetone as a marker of energy balance: An exploratory study in healthy humans. Nutrition & Diabetes, 8(1), Article 50. https://doi.org/10.1038/s41387-018-0058-5
  13. Kistenev, Y. V., Borisov, A. V., Zasedatel, V. S., & Spirina, L. V. (2021). Diabetes noninvasive diagnostics and monitoring through volatile biomarkers analysis in the exhaled breath using optical absorption spectroscopy. The Review of Diabetes Studies, 18(4), 213–225.
  14. Miekisch, W., Schubert, J. K., & Noeldge-Schomburg, G. F. E. (2004). Diagnostic potential of breath analysis – focus on volatile organic compounds. Clinica Chimica Acta, 347(1-2), 25–39. https://doi.org/10.1016/j.cccn.2004.04.023
  15. Fischer, S., Stötzer, R., Rohn, S., & Schwaiger, J. (2015). Physiological variability in volatile organic compounds (VOCs) in exhaled breath and released from faeces due to nutrition and somatic growth in a standardized caprine animal model. Journal of Breath Research, 9(2), Article 027108. https://doi.org/10.1088/1752-7155/9/2/027108
  16. Filipiak, W., Mochalski, P., Filipiak, A., Ager, C., Cumeras, R., Davis, C. E., Agapiou, A., Unterkofler, K., & Troppmair, J. (2016). A compendium of volatile organic compounds (VOCs) released by human cell lines. Current Medicinal Chemistry, 23(17), 2112–2131.
  17. Mazzatenta, A., Pokorski, M., & Di Giulio, C. (2015). Real time analysis of volatile organic compounds (VOCs) in centenarians. Respiratory Physiology & Neurobiology, 209, 47–51. https://doi.org/10.1016/j.resp.2014.12.014
  18. Parr-Cortes, Z. (2020). How do dogs respond to olfactory changes associated with human health and stress? [Thèse de doctorat, University of Bristol]. Bristol Research Information.
  19. Curry, E., Skogen, M., & Roth, T. L. (2021). Evaluation of an odour-detection dog for non-invasive pregnancy diagnosis in polar bears Ursus maritimus: Considerations for training sniffer dogs for biomedical investigations in wildlife species. Journal of Zoo and Aquarium Research, 9(1), 1–7. https://doi.org/10.19227/jzar.v9i1.568
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