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Understanding VOCs – What They Are and Why They're Invisible but Critical in Hunting

Volatile Organic Compounds (VOCs) are small organic molecules that evaporate easily at room temperature. In the human body, they're produced by numerous metabolic processes: digestion, energy production, inflammation, microbial activity, and more. VOCs are found in breath, sweat, urine—even in blood when it's exposed to air. Altogether, the human body emits hundreds of different VOCs on a continual basis. One study mapping the "human volatilome" has identified over 1,849 distinct VOCs across our breath, sweat, and other secretions1.

 

Some of these compounds are well-known in the field of medical diagnostics. Acetone, for example, is a byproduct of fat metabolism—its levels rise in the breath when fasting or following a ketogenic diet. Isoprene is another common VOC, derived from cholesterol turnover in the body. Others include ethanol, methanol, formaldehyde, hydroxyketones, and a variety of naturally occurring hydrocarbons like benzene. These metabolites are always present, though their levels can fluctuate based on diet, health status, breathing rate, or physical activity2.

 

What makes VOCs so powerful as scent markers is their volatility—and the astonishing sensitivity of olfactory receptors in wild game and hunting dogs. Although the typical concentration of VOCs in exhaled air is extremely low (often in the range of a few dozen or hundred parts per billion, or ppb), this is more than enough for animals with keen noses. Dogs, for instance, can detect a single volatile compound at concentrations as low as one part per trillion (1 ppt)—millions of times more sensitive than standard lab instruments. To put that in perspective, it’s like detecting one drop of water in 20 Olympic-sized swimming pools. By contrast, the human nose typically only picks up VOCs at concentrations of several parts per million (ppm)—thousands of times more concentrated3.

All of these VOCs form, without our awareness, a kind of constant "scent signature." Chemically speaking, this is known as the human volatilome: the full range of volatile emissions unique to an individual. This volatilome shifts with age, diet, emotional state, and more. Researchers have even shown that each person’s VOC profile is unique—and can be influenced by genetic factors, like the specific HLA alleles a person expresses. In hunting, this means that each hunter carries an individual scent signature—just as distinctive as a worn garment or trail left behind.

 

Why is this invisible factor so crucial to hunting? Because even a hunter who appears "clean" to the human eye or nose will still be detectable to game. Deer, wild boar, and similar species inhabit a chemical world—they rely on molecules suspended in the air4. More than 80% of what these animals "smell" comes from a person’s breath. Every exhale releases a mixture of VOCs that—even in trace amounts—can raise red flags. Compared to that, the scent of sweat plays a much smaller role. It’s not absent, but the most meaningful information comes from inside the body.

 

This reality is often unknown to hunters. Research articles circulate the figure of "80% of scent comes from breath," which can be surprising. This figure does not come from a single study on a panel of hunters, but it is corroborated by physiology and the science of clothing. In fact, the air you exhale is a continuous flow rich in volatile organic compounds (VOCs). In contrast, clothing acts as a barrier that absorbs and retains skin VOCs, reducing their release into the environment5.

 

Furthermore, the wind acts as a vector that projects these respiration molecules over long distances, massively amplifying their scent signature. The breath, a "jet of air rich in hundreds of molecules," can create a true "scent trail"6. Due to the retention of skin odors and the amplification of respiration odors by the wind, the skin's contribution is largely eclipsed. This means that the scent animals most detect is the one coming from your breath.


The animal's sense of smell has the ability to "accumulate" these signals over time. Dogs, for example, are capable of detecting odors at concentrations 100,000 times lower than humans. A dog can follow a trail for several days because VOCs are deposited on vegetation and the ground. This means that even a hunter who believes they are discreet leaves behind a persistent chemical trail7.
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In conclusion, understanding VOCs means recognizing that human scent is largely invisible to us—but highly conspicuous to wildlife. Every hunter eventually learns that it’s your breath doing most of the talking. Exhaled VOCs form the base of this invisible “language of scent”—they are our natural perfume in the forest, whether we like it or not. Ignoring their presence means risking detection, even when you think you’re fully concealed. That’s why, in hunting, the first precaution isn’t just masking scent—it’s understanding the biology behind how scent is produced in the first place.

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References

 

1- 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

2- 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.
3- 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.

4- 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

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- 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

7 - 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

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