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nose
nostril

When it comes to eyes and ears, pairs make sense. Paired eyes give us stereo vision, which allows us to see objects in depth, and paired ears give us stereo hearing, which allows us to detect the direction a sound is coming from. The reason for paired nostrils, however, is a little less obvious. While there is no such thing as stereo olfaction (smelling), the pairing of our nostrils is not just for show.

The nose is the focus of our sense of smell, but it’s also where we draw in much of our oxygen. Our nostrils have evolved to perform both roles, although each nostril prefers one role over the other at different times. At any given moment, one nostril may draw in more air than the other, whereas the other nostril will draw in less air, which allows it to better pick up certain scents in the environment. Even in breathing mode, the high-flow nostril can still detect a scent, but the scent will spread throughout the nostril’s sensory receptors quickly. If the scent is a kind whose microscopic particles can dissolve quickly in the fluid covering such receptors, the high-flow nostril will pick it up; if the scent is a kind whose particles can’t dissolve quickly, that nostril may detect it as fainter. In contrast, the low-flow nostril is likely better at dissolving (and hence detecting) scent particles, because it has the time to do so. Studies have shown that each nostril can switch between breathing dominance and smelling dominance several times per day, which can be helpful—for example, when there is nasal congestion caused by the common cold.

John P. Rafferty
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dog
nose
smell

Dogs have wet noses mainly to enhance their sense of smell. The moisture on the nose traps scent particles in the air, making it easier to detect and process smells. A dog’s ability to detect scents plays a crucial role in how they explore and understand its surroundings.

A dog’s nose is far more sensitive than a human’s. The wet surface helps dissolve tiny scent particles, allowing the dog’s olfactory system to pick up a wide range of smells. This strong sense of smell helps dogs with tasks such as tracking missing people or detecting drugs and explosives.

Another reason for a dog’s wet nose is thermoregulation. Dogs don’t sweat like humans. Instead, they lose body heat through panting, sweating through their paw pads, and the moisture on their nose. The wetness helps cool the blood in their nose, which can lower their overall body temperature.

A wet nose can also be an indicator of a dog’s health. While not a sure sign, an extremely dry nose might suggest the dog is dehydrated or unwell. A wet nose is often linked with good health, but it’s normal for a dog’s nose to change between wet and dry during the day based on weather and activity.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Mindy Johnston.