Dr. David Dorman is a professor of toxicology in the N.C. State College of Veterinary Medicine. Here he explains what makes a dog’s sniffer so special. Questions and answers have been edited.
Q. Why do dogs have wet noses?
A. There are several reasons. First, many dogs can lick their noses, which can help keep their noses moist. Second, unlike people, dogs have very few sweat- producing glands. Dog sweat glands are found mostly on their foot pads, but a smaller number are also found near their noses. However, some dogs’ noses will appear dry to the touch, but this is not something to be concerned about.
Q. Is it true that dogs can be identified by their nose prints?
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A. Like human fingerprints, each dog has a unique nose print. Some kennel clubs have used dog nose prints for identification, and there are videos from the early 1930s showing how these nose prints are collected.
Q. How are dogs able to detect cadavers, drugs, and bombs?
A. You might have encountered the unpleasant smell of a dead animal as you were driving down the road. As a cadaver decomposes, it releases a large variety of volatile chemicals. Although we can’t see them, these volatile chemicals, like smoke from a chimney, will form a plume that gets dispersed in the air. When we breathe, these volatile chemicals are delivered to specialized nerve cells (olfactory neurons) that are found within the nose.
Your dog will detect an odor much earlier than you do, since your dog’s nose is 10,000 to 100,000 times more sensitive than a human’s! Dogs have over a thousand times more olfactory neurons than we do. Dogs trained for scent detection also have long noses that very efficiently deliver air to these olfactory neurons. This allows them to detect trace amounts of chemicals in the air that will go undetected by us. Other animals are trained for scent detection as well. For example, some types of rats are being used in Africa and Asia to detect landmines.
Q. Can dogs use their noses to sense human emotions, like fear? What about illnesses, like cancer or epilepsy?
A. Scientists have recently shown that people, like other animals, can use alarm pheromones to communicate danger. These odor cues can be detected by other people, so it’s very likely that dogs can detect and respond to these cues too.
There are reports that dogs can be used to detect cancer or alert people to an oncoming seizure. However, the scientific literature is generally lacking with respect to the accuracy and reliability of these scent-detector dogs. Our laboratory has recently examined whether trained scent dogs could reliably detect cancer found in other dogs. We trained the scent dogs to signal whenever a urine sample came from a dog with a form of urinary bladder cancer. To verify our training was effective, we used unfamiliar urine samples and we made sure that the tester did not know whether the sample came from a normal dog or one with cancer. This precaution is important because dogs respond to subtle cues from people. Our results were not as rewarding as we hoped, but we had a limited number of dogs available to train. It's very possible we missed finding dogs that would have been good cancer detectors.