Dogs’ noses are so cold because they are ultra-sensitive heat detectors, a new study has confirmed.
European researchers found that when ambient temperature is 86°F (30°C), a dog’s rhinarium – the bare end point of the nose – is some 5°C (9°F) cooler.
This helps breeds such as retrievers to detect often very faint heat sources, such as the presence of a small mammal, from five feet away.
The team studied three dogs – Kevin, Delfi and Charlie – who were trained to identify which of two identical four-inch wide objects had been heated to around 22°F (12°C) warmer than room temperature.
Thermograph of a golden retriever in the shade at 80°F (27°C) ambient temperature. The colour scale on the right is in °C and can be used to read out approximate temperatures. Note the warm tongue and the cold rhinarium (hairless nose tip)
The team used a Golden retriever, a Nova Scotia Duck Tolling Retriever and a mixed breed.
‘All three dogs could detect stimuli of weak thermal radiation in double-blind experiments,’ the study said.
‘All stimuli of radiating heat used in our experiments were too weak to be felt by human hands, even at very short distances. We had to touch the surfaces to feel the warmth.’
The team say the rhinarium is ‘prominent and richly innervated’, meaning it is supplied with nerves, which suggests a sensory function.
The warm stimulus presented to the dogs elicited increased response in the left somatosensory association cortex of the brain. Functional MRI (left) on a reconstructed 3D image of the dog’s brain showing increased activity, and right shown in a horizontal slice
Compared to nose-tips of herbivorous hoofed animals, those of dogs are considerably colder.
‘We hypothesized that this coldness makes the dog rhinarium particularly sensitive to radiating heat,’ the team say.
In addition, the scientists used functional magnetic resonance imaging on 13 awake dogs, which measures brain activity 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.
The warm stimulus caused increased responsiveness in the brain, they found.
‘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 behaviour 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, postdoctoral researcher at the Department of Ethology, Eötvös Loránd University, Hungary.
Thermograph of golden retriever pictured choosing a warmer object over a colder one. The dog’s rhinarium – the naked, wet skin surface at the tip of the nose – works as an infrared sensor which can sense weak thermal radiation
A dog’s nose also 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 dispute this theory because the rhinarium has such a small surface area compared to the rest of the body.
Researchers say the role of the wet rhinarium in regulation of heat is unlikely because of its small size, disproving previous theories, and is used, as above, to detect the presence of small mammals
Panting is also a previously established technique by dogs to release heat.
‘Furthermore, 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.’
The research team from Sweden’s Lund University and the Eotvos Lorand University in Hungary had their research published in Scientific Reports.