Photo of Smarties candies sorted by color

Why Scent Travels

Why does scent disperse, instead of just staying inside the hide?

It’s a law of nature. Scent spreads out. Read on if you want to learn more about the science behind scent dispersion, and what it has to do with the Smarties in the picture.


Scent disperses because of the Second Law of Thermodynamics. Basically, every isolated system tends to degenerate towards a more disordered state over time. This is known as “entropy”, or disorder. For example, entropy is why water falls from the top of the waterfall into a more chaotic pattern at the bottom (and it will never flow back up). Whether you consider a system of solids, liquids or gasses, all inevitably disperse towards a more disorderly state.

If entropy seems complicated at first, let’s picture a simple example that most people can relate to. If you sort a package of Smarties into colors and then shake the container, the Smarties spread out into a more disordered state. The colors inevitably get mixed up. And once things become disordered, it’s irreversible. You instinctively know that no matter how long you keep shaking the container, the Smarties will never spontaneously return to groups of organized colors.

Similarly, if you pour red wine into a bathtub full of water, the wine spreads out in all directions into a more disordered state. The longer you leave it, the more it intermingles with the water, until it reaches equilibrium (where the concentration of wine is equalized throughout). And the process will never flow backwards.

In exactly the same way, after you place an orderly hide in a container, it moves towards an increasingly diffuse and chaotic state, dispersing into the environment.


Essential oils used as nosework target odors exist in all states: solid, liquid and gas.

When you purchase essential oils, they come as liquids in an airtight bottle. Over time, some solid crystals may form, especially when:

  • Your bottle has an orifice reducer (a plastic piece in the lid with a hole designed to dispense a drop at a time instead of a continuous stream), which can hold and accumulate sludge unless you wipe it off after each use,
  • The environmental temperature is colder, and/or
  • Most notably with inherently thick/dense oils such as Myrrh and Vetiver.

Whenever you open a bottle of essential oil, many of the molecules quickly evaporate into gas, which travels through air. When you smell most scents and odors, you are actually smelling Volatile Organic Compounds (VOCs) that travelled through the air and into your nose. VOCs are organic chemicals produced by plants, which have high vapor pressure and evaporate easily at room temperature. Therefore, many VOC molecules travel from the hide, through the air, to your nose, where the odor can be detected by your olfactory system.


In conclusion, whenever you place a hide inside a box, scent disperses into a more disorderly state over time, increasing the entropy, according to the 2nd Law of Thermodynamics. The longer you leave the scent, the more the odor will spread out, until it reaches equilibrium. Volatile organic compounds (VOCs) in the air can then be detected by canine and human olfactory systems.

WHY scent disperses is fairly complicated. But in reality, scent dispersion is what makes it possible for a dog to detect odor and track it back to source! If scent didn’t travel, it would be a lot more difficult to find the pinpoint source.


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