The sense of smell is the most important of all the senses in dogs, because they use their nose to interpret their environment. Dogs with poor eyesight or hearing can still find their way around very well by sniffing.
Dogs are known and sought after for their nose. They are often used by police or rescue services to smell people or dangerous substances. A dog's ability to smell depends on many things, such as weather conditions, artificial scents in its immediate environment like perfume or petrol, or strong-smelling aromas like freshly cut grass that overpower its nose and distract it from other, more subtle smells. All these factors influence how far a dog can perceive a particular smell.
There is no set limit to the distance a dog can smell. Reportedly, there have been dogs that could smell from ten metres to one and a half kilometres. However, these are isolated cases where the external circumstances were particularly favourable and they do not describe how far any dog can smell. But the distance is also not what is special about the dogs' sense of smell. What is remarkable is rather what the dog is able to sniff out. While humans smell the aroma of freshly baked bread in a bakery, the dog picks up the aroma of every ingredient. While we can just detect if there is a teaspoon of sugar in a cup of coffee, the dog can smell the same amount of sugar in millions of litres of water.
A dog's sense of smell is 100,000 times finer than a human's. The human brain is larger than the dog's, but the part of the brain that controls the sense of smell is 40 times larger than that in humans.
A dog can smell and breathe at the same time, the air goes in two different directions when inhaled. One part reaches the lungs and supplies the body with oxygen, the other part reaches the sense of smell. In the sense of smell, the air is filtered and thus examined for substances it contains. Through receptors, the brain receives information about what the dog has just smelled. When exhaling, the used air is expelled through side openings in the nose so that the dog can simultaneously take in new smells again. The ability to smell continuously and move the nostrils independently allows the dog to determine the origin of the smell.
When the dog meets a conspecific, it determines by sniffing whether it is a male or a female, what substances the dog has come into contact with and what it has eaten.
Studies suggest that a dog can smell disease. This research is supported by experiments in which dogs have detected blood sugar drops, epileptic seizures or cancer in 90% of cases.
