Working Hard, Sniffing Harder

In the previous post, we discussed the olfactory world of the dog, a world which is populated by millions of scents and odors that humans will never be able to detect. Today, we are going to look at how this heightened sense has developed, and how it can help us gain important insight into our own environment and health. Sniffer dogs, or odor detection dogs, are used in a wide variety of fields including military, police, and medical, but what exactly are they able to do, and how do they do it?

Flickr user SuperFantasticBloodhound portraitCC BY 2.0

All dogs are natural born sniffers – and that is no accident. Many early dogs were selectively bred to have sniffing abilities that outpaced even their wolf ancestors (Polgár et al., 2016). These dogs were used primarily for hunting and tracking. Not as many working dogs actively hunt prey today, but this selective breeding can still be seen in many modern dogs. Blood hounds, for instance, have long ears and floppy jowls which help pull odors from the ground up toward the nose. Their unusually wet noses also help dissolve odors from the air into the nasal passages (Gadbois & Reeve, 2014). But what makes the difference between a pet and a working odor detection dog? All sniffer dogs are certainly not blood hounds. Many are Labrador Retrievers, German Shepherds, or even mixed breeds. A large amount of a dog’s success comes from rigorous training and a solid handler relationship, but recent research suggests that variations in the genetic makeup of canine olfactory receptor (OR) cells may set some dogs apart from the pack. Most OR genes have allelic variations, some of which are breed-specific, and some of which can appear regardless of the dog’s breed. One of these is a transition from the base guanine to the base of adenine in locus 529 of the cOR9S13 gene. Dogs with this altered genetic sequence performed more accurately on scent-detecting tasks than dogs without this substitution (Lesniak et al., 2008).

Al Bright, Air Force Military Working Dog 160914-F-BO631-1112, marked as public domain, more details on Wikimedia Commons

In our last post, we discussed Jacobson’s organ, which dogs use to process volatile compounds in the air, typically pheromones. Now, however, research suggests that this organ is what enables them to detect the presence of cancer in human subjects, long before physical symptoms appear (Pirrone & Albertini, 2017). In several ground-breaking studies, researchers have shown that dogs are capable of sniffing various types of cancer from breath, urine, and other noninvasive measures at far higher than chance percentages. More than 30 volatile organic compounds (VOCs) have been identified in the breath of cancer patients and healthy controls, but the VOCs may be present in different combinations and quantities. This makes training dogs to detect a single VOC, or even one combination, unrealistic. Researchers are working to distinguish which VOCs are present when dogs alert, and some, including ethyl acetate and 2-pentanone, seem promising, but these alone are not enough to positively provide a diagnosis, and these appear in some quantity even in healthy patients (Pirrone & Albertini, 2017). Currently, dogs are trained with a wide variety of cancerous and noncancerous samples, but what chemical compounds the dogs specifically detect remains unknown.

Similar training is used for dogs used to detect threats, such as explosives, narcotics, or certain weapons. There are no universal threat detection dogs; instead each is trained to detect a specific odorant or combination of odorants through stimulus-reward training. Specific testing of these dogs in comparison to controls has shown that these dogs rely far more on their olfactory senses than non-trained dogs. They tend to use and trust their noses even in well-lit room with plenty of visual information (Gazit & Terkel, 2003). Although not a genetic evolution, this is another example of how humans control and shape dog behavior.

At the beginning of this post, we talked about OR polymorphisms which may make some dogs naturally better at detecting certain odors than other dogs, but what about dogs with average noses? Researchers at Auburn University may have a solution. They have discovered that adding
zinc nanoparticles to odorants has a positive effect on canine sniffing ability. Using fMRI studies, researchers observed that dogs who inhaled zinc nanoparticles along with different odorant samples had increased activation of the olfactory bulb and related areas (Jia et al., 2016). This could decrease the amount of an odorant needed to alert the dog, and could help ensure positive identifications. While this is a new technique in a constantly-evolving field, this may help increase the accuracy of dogs trained to work in medicine, security, wildlife-conservation, and more.


Gadbois, S., & Reeve, C. (2014). Canine Olfaction: Scent, Sign, and Situation. In A. Horowitz (Ed.), Domestic Dog Cognition and Behavior (pp. 3–29).

Gazit, I., & Terkel, J. (2003). Domination of olfaction over vision in explosives detection by dogs. Applied Animal Behaviour Science, 82(1), 65–73.

Hackner, K & Pleil, J. (2017). Canine olfaction as an alternative to analytical instruments for disease diagnosis: understanding “dog personality” to achieve reproducible results.

Jia, H., Pustovyy, O. M., Wang, Y., Waggoner, P., Beyers, R. J., Schumacher, J., & Deshpande, G. (2016). Enhancement of Odor-Induced Activity in the Canine Brain by Zinc Nanoparticles: A Functional MRI Study in Fully Unrestrained Conscious Dogs. Chemical Senses, 41(1), 53–67.

Lesniak, A., Walczak, M., Jezierski, T., Sacharczuk, M., Gawkowski, M., & Jaszczak, K. (2008). Canine Olfactory Receptor Gene Polymorphism and Its Relation to Odor Detection Performance by Sniffer Dogs. Journal of Heredity, 99(5), 518–527.

Pirrone, F., & Albertini, M. (2017). Olfactory detection of cancer by trained sniffer dogs: A systematic review of the literature. Journal of Veterinary Behavior, 19, 105–117.

Polgár, Z., Kinnunen, M., Újváry, D., Miklósi, Á., & Gácsi, M. (2016). A Test of Canine Olfactory Capacity: Comparing Various Dog Breeds and Wolves in a Natural Detection Task. PLOS ONE, 11(5), e0154087.

Leave a Reply

Your email address will not be published. Required fields are marked *