Dogs’ noses are quite cold because they are ultra-sensitive heat detectors, a new study has confirmed.
While it has been widely assumed the phenomenon is related to body temperature regulation, European researchers have now revealed that the tip of the nose serves an important sensory function.
They found that when the ambient temperature is 30°C (86°F), a dog’s rhinarium – the bare endpoint of its nose that is full of nerves – is some 5°C (9°F) cooler.
This helps breeds such as retrievers to detect even the faintest heat sources, such as the presence of a small mammal, from five feet away.
The team trained three dogs – a Golden Retriever named Kevin, a Nova Scotia Duck Tolling Retriever named Delfi, and a mixed breed called Charlie – to distinguish between two identical four-inch wide objects based on radiating heat.
The ‘neutral’ object was about room temperature and the warm object was heated to around 12°C (22°F) above room temperature.
All three dogs were able to sense weak thermal radiation from the warm object from a distance of five feet, despite the difference in temperature being too small for humans to detect without touching.
‘All stimuli of radiating heat used in our experiments were too weak to be felt by human hands, even at very short distances,’ the researchers wrote.
‘We had to touch the surfaces to feel the warmth.’
The experiment shows that dogs’ rhinariums serve a sensory function – they detect heat – rather than just regulating their body temperature.
To further prove their theory, the scientists used functional magnetic resonance imaging to measure brain activity in 13 awake dogs by detecting changes associated with blood flow.
For this part of the study, the team enlisted the help of five golden retrievers, four border collies, one Australian shepherd, one Chinese crested and two mixed breeds.
They found that putting a warm object in front of the dog’s nose caused increased responsiveness in the brain.
‘From the two, complementary experiments, we can conclude that dogs are indeed capable of sensing thermal radiation emanating from warm-blooded animals, use this sensory information for directed behavior that could be relevant for hunting, and that a specific region of the somatosensory system is activated by such infrared radiation,’ said lead author Anna Bálint, a postdoctoral researcher at the Department of Ethology, Eötvös Loránd University, Hungary.
A dog’s nose changes temperature depending on the surrounding ambient temperature.
If the outside temperature is freezing – 32°F or 0°C – a dog’s nose will be around 46°F. However, if the surrounding temperature is 59°F (15°C), the pooch’s nose is around the same.
While it has been widely assumed the phenomenon is related to body temperature regulation, the researchers questioned the theory because the rhinarium has such a small surface area compared to the rest of the body.
Panting is also a previously established technique by dogs to release heat.
‘If a dog is exposed to moderate heat stress and starts to pant, it extends the tongue from the open mouth,’ the researchers say.
‘The tongue is wet and warm, despite the airflow generated by panting, and is thus effectively dissipating surplus body heat by radiation and evaporation.
‘The rhinarium, however, remains cold and is therefore ineffective.’
Rhinarium is the hairless skin area surrounding the nostrils in certain mammals.
It’s part of the olfactory system and is therefore associated with the sense of smell.
Animals with rhinarium – which also include cats, walruses, elephants, and lemurs – are said to have a more acute sense of smell.
It has also been found to act as a wind detector, allowing animals to detect the direction from which certain smells have come from.
The research team from Sweden’s Lund University and the Eotvos Lorand University in Hungary had their research published in Scientific Reports.