Which animal has the best sense of smell in the world?
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There is no scientifically established winner: the brown bear is often cited as the mammal with the finest sense of smell, ahead of the dog, thanks to a much more extensive olfactory mucosa, but no protocol allows objectively comparing all species with each other.
Why a classification is illusory
The most cited estimate is based on the surface area of the olfactory epithelium: that of the brown bear would be approximately one hundred times greater than that of the dog, itself already much larger than that of humans. But this surface area is only an indirect indicator: the real sensitivity also depends on the number of functional olfactory receptors, their genetic diversity and the way the brain processes these signals in the olfactory bulb.
Studies that measure detection capacity use different molecules depending on the species tested: traces of blood, pheromones, sulfur compounds, explosives or food substances. A dog trained to detect explosives and a bear searching for a carcass several kilometers away are not compared on the same molecules or the same concentration thresholds, which makes any numerical hierarchy fragile.
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The experimental protocols also differ greatly: laboratory tests with food reward for the dogs, field observations for the bears following the odors of carrion over several kilometers. These conditions do not measure the same thing and make a numerical comparison unreliable from a methodological point of view.
What we really know about the brown bear
What is solidly documented is that smell is the brown bear's dominant sense, far superior to its sight or hearing. It allows it to locate carrion several kilometers away, to detect hives, or to spot conspecifics during the reproduction period. This ability is explained by a proportionally large olfactory bulb and a high number of olfactory receptor genes, but it is not enough to establish an indisputable “world record” between species.
