In the hunting world, it’s often said that around 80% of the scent detected by game comes from human breath. This commonly cited rule of thumb may seem surprising and deserves a closer look from a scientific perspective. At first glance, it’s easy to assume that sweat or body odor plays the dominant role. But research and field experience increasingly suggest that volatile organic compounds (VOCs) exhaled through the lungs are what truly drive the “chemical dialogue” between hunters and big game1.
To understand why, we need to look at basic human physiology. Every organ in the body constantly produces metabolic byproducts. Many of these are soluble and circulate through the bloodstream. As blood flows through the lungs, it undergoes a vital exchange: carbon dioxide (CO₂) and VOCs are offloaded from the blood and expelled through exhalation, while oxygen is absorbed. Each liter of breath we exhale contains CO₂, water vapor, and a host of trace compounds produced by our metabolism, such as acetone (a byproduct of fat metabolism), isoprene (linked to cholesterol turnover), alcohols, hydrocarbons, methanol, and others. These VOCs exist at extremely low concentrations, typically in the parts-per-billion (ppb) range, but they form a unique chemical signature2.
By contrast, body odor from sweat and skin mainly results from microbial activity. Skin bacteria break down fatty acids and peptides, producing sulfides, volatile fatty acids, indoles, and other smelly compounds. However, these odors are often released more slowly and are partially absorbed by clothing or dispersed in the environment. In wooded areas or dense underbrush, skin-emitted VOCs tend to stay localized or get filtered by vegetation, whereas exhaled air rises and can settle on canopy leaves or damp ground. In short, it’s your breath that game animals are most likely to detect.
Studies in scent detection, especially involving dogs, support this. Scientific reviews have identified at least 874 distinct VOCs in the breath of healthy individuals, with over 1,849 documented across breath, sweat, saliva, and urine1. Breath, in particular, is a chemical snapshot of internal physiology. These compounds enter the atmosphere with ease due to their low boiling points. Meanwhile, skin-emitted odors are often less volatile unless physically transferred (such as by touching or contact with clothing). The oft-cited “80% rule” isn’t from a single peer-reviewed study, but it aligns with practical experience: most of the scent information game animals pick up comes from your lungs, not your deodorant.
In terms of persistence, human scent can linger in the environment for an extended period. Scent traces on soil or grass can remain detectable for many hours, even if the person is motionless. Over time, volatile organic compounds (VOCs) fade or disperse, but game animals and dogs can still track older trails thanks to lingering chemical residues on vegetation. Scent compounds are retained even longer on clothing or footwear, remaining detectable for weeks or even months. In most cases, the source of this lingering scent is breath, through condensation or indirect transfer. Dogs, for example, can often track these odors more than 72 hours later.
