How Dogs ‘Hear’ Through Smell

1 A Nose Above Our Own

A dog usually turns to smell first, then sight and hearing, and taste last. Like us it reads the surroundings visually — but where we have around 500 olfactory receptors, a dog has roughly 300 million, and its scent-detecting membrane is about 150 cm² against our 5 cm²: the difference between a newspaper and a postage stamp. A trained working dog can even sniff out certain diseases — warning of seizures or high and low blood sugar, and detecting some cancers. Studies show that, given samples of human breath, urine, or stool, dogs can pick out ovarian, lung, bladder, colon, or breast cancer patients with better than 90% accuracy.

2 Reading the World by Scent

We open our eyes on the world; a dog uses its nose. We can be fooled by a smile, but a dog smells tension and the scent of a quickening heartbeat, and reads emotion and intent from it — proof that what you see is not always what is true. When meeting someone, we might shake hands or hug; when a dog approaches, it identifies the other by scent and quickly works out the animal’s sex, age, and where it came from and is going.

Many owners know the scene: you come home to a mess, anger rising, and before you can blow up the dog has already slipped away. Your shifting mood changes your temperature, heartbeat, and breathing, and those changes travel through the air to the dog.

3 Greeting and Remembering by Smell

They say a dog fed for three days remembers you for three years, and a dog’s loyalty is not to be underestimated — even a few days of care or a few meals is enough for it to remember you. This is why a dog that strays can find its way home by scent: smell is a dog’s main memory, and the scent on its owner and their clothes is quickly learned.