Asked by: David Watt, Cumbria
A human nose has about five million olfactory receptor cells in it. In a dog’s nose, these cells are packed together with 10 times the density, and a large dog breed has a nasal cavity that is about four times the size of a human one, giving upwards of 200 million receptor cells. Tracking dogs follow the scent trail of a particular individual, which is mostly skin cells because they are heavy enough to fall to the ground and mark the route.
Mountain rescue search dogs are usually air scenting dogs, however. That means they’re trained to find a human within a large area when there isn’t an initial point to pick up a trail from. Air scenting dogs search with their nose in the air and follow volatile and aerosolised particles that can be carried several miles in the air. These particles comprise a mixture of natural human secretions such as sweat, body odour and pheromones, as well as artificial smells from deodorant, perfume, make-up and clothing.
Air scenting dogs aren’t trained to discriminate between different scents; they will find any human that’s not their own handler. They work by following the ‘scent cone’ that spreads from the search target, on the wind. But scents will also cling to undergrowth as the target brushes past, which can sometimes even allow dogs to find targets that are downwind of them.