A wet nose is a staple of a good dog, ever twitching, seeking scents in the air that are invisible to the paltry human schnozz. It’s often said that a wet nose is the sign of a healthy dog, and while this is true to some extent, there’s another explanation as to why dogs’ noses are wet.
Smell is hugely important to canines. The portion of a dog’s brain dedicated to processing smell is 40 times larger than ours, proportionally speaking, and they’re adorned with 300 million olfactory receptors in their noses. In general, compared to humans, their sense of smell is at least 10,000 times better than ours.
Research has even found that dogs may be able to use their smell to form a mental picture of the world around them, so keeping this sense keen is clearly crucial for their success. But can you guess that hampers the smelling power of pooches? That’s right, a dry nose.
To keep those 300 million olfactory receptors working properly, dogs secrete mucus that travels from inside the nasal cavity to coat the rhinarium (the twitchy outside part of the nose that owners are all too familiar with having poked in their faces). Smell is the result of these receptors picking up chemicals drifting in the air, and when a dog’s nose is wet it’s better able to capture the chemicals and process them.
Given that canines use smell for identifying prey, predators, and communication, having a functioning snoot really is a matter of life and death so it figures that they’ve evolved an acute sense of smell and physiological responses to keep it sharp. Behaviorally, they will also frequently lick their nose as this helps to keep the mucus evenly coated across the nose and adds an extra spritz of moisture.
Another explanation as to why dogs' noses are always wet is linked to how they sweat. Being covered in fur, sweating through the skin like humans do wouldn’t be very effective. Instead, they sweat through their paws and a small amount of sweat is also released by the nose.
Not only does this help to keep a dog’s nose wet, but it also keeps it cool, which research has found serves another purpose: Regardless of smell, dogs can also use their noses to detect heat.
The 2020 study wanted to investigate dogs' noses because they’d hypothesized that the colder noses of carnivores like dogs (compared to the warmer noses of herbivores) may have evolved as a kind of infrared sensor. To do so, they trained three dogs to identify hot objects, and found that they were able to tell hot and cold objects apart even when they couldn’t smell anything.
So, why are dogs’ noses wet? All the better to smell you with, my dear.