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How Can Dogs Sniff Out Cancer?

Today we would like to discover some more details about dogs who are putting their sniffers to work for a noble cause: detecting illnesses, in particular dogs who sniff out cancer. How do dogs detect cancer? Does cancer have a specific smell that dogs can discriminate from other smells? We have found some interesting findings on the subject, so we’ll be sharing them this Thursday in honor of our dog’s talented sniffers. So let's take a look at our dog's powerful sniffers, how they can help in detecting cancer and the type of training cancer-detecting dogs must go through.

dog nose detects cancer

A Powerful Sniffer

In order for dogs to detect cancer, several conditions must be met: the dog must have a sense of smell that is powerful enough to detect its smell, the cancer must release a distinctive smell that makes it stick out from other smells, and then, the dog must be properly trained to let us become aware of it.

When it comes to having a powerful sense of smell, there's no doubt that dogs have powerful sniffers. While humans have only a mere 5 million olfactory receptors, it's estimated that dogs have an outstanding 300 million. On top of that, the part of the dog's brain responsible for analyzing odors is 40 times greater than ours.

In the book "Inside of a Dog, What Dogs See, Smell, and Know," Alexandra Horowitz, a cognitive scientist and researcher at Barnard College, offers a good example of how powerful those sniffers really are: while we are barely capable of noticing that our coffee has a teaspoon of sugar added to it, a dog is capable of detecting one teaspoon of sugar in a million gallons of water. That's quite amazing, considering that that's about the size of two Olympic-sized pools!

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Does Cancer Have a Smell?


So dogs have a powerful sense of smell, there's no bones about that, but does cancer emanate a distinctive smell? This is not an easy question to answer since our poor sense of smell may not be powerful enough to detect such smells especially at its earliest stages.

Sure, there are nurses and oncologists who claim to have smelled cancer in their patient's breath, but this appears to occur mostly in the most advanced stages.

While there is some anecdotal evidence coming from dog owners claiming that their dogs showed a strong interest towards a specific spot or area on their skin, which was later found to be cancer, the good news is that more and more promising, and most of all, "palpable" evidence is coming through.

Interesting details come from one of the latest studies published in the Journal of Urology. In this study, two female German shepherds trained for Explosion Detection were trained to identify specific volatile compounds in the urine samples of patients suffering from prostate cancer. The dogs were then tested on 362 patients suffering from prostate cancer and 540 healthy individuals that did not have cancer and the results looked promising!

Of course, further studies will be needed to further prove any potential predictive values for future use of dogs for this purpose, but overall, the results were quite remarkable with both dogs showing promising abilities in detecting compounds associated with prostate cancer.

dog sniff

An Instinctive Behavior

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When it comes to putting their powerful sniffers to work, dogs may retain an instinctive tendency to become interested in smells that suggest disease. This tendency may date back to the days when canines had to mostly fend for themselves.

Predators by nature are attracted to prey animals that are sick or injured in some way, explains the InSitu Foundation, an organization that has been dedicated to scientifically training dogs to detect early stage cancer in humans for over 12 years.

Sick, slow and injured animals are the most vulnerable and the easiest to be caught. After many years of hunting, predator animals learned to associate that "sick scent" with an easy meal so they're naturally drawn to it.

Even when dogs didn't specifically hunt, but were acting more as scavengers, they were (and continue to be) attracted to the smell of sickness, disease or something rotting as this played a big role in their survival.

Perfecting the Training

dog nose

Just because dogs are naturally drawn to certain smells, doesn't mean that they are born knowing what to do when it comes to detecting specific odors.

Dogs require extensive training in order to learn to detect and alert about the presence of compounds suggestive of cancer.

According to the InSitu Foundation the process is similar to training dogs to detect bombs and narcotics. The odor is simply paired with a high value reward, in a similar fashion as predators learn to pair the smell of a sick prey with an upcoming meal. Through repeated pairings, the conditioning process teaches dogs to become highly motivated to seek out that smell.

However, it's not that easy. If breath is being analyzed, the specific compound must be isolated as the dog needs to learn how to discriminate it from other smells in breath. This would require exposure to many samples so that the dog can be taught exactly what to look for.

Finally, the dog must learn to alert of his findings. Dogs may stop and sit down by the sample or they may lick the bottle to communicate that they have positively detected the scent of cancer cells. So things look promising so far in the dog-cancer -detecting department.

According to UC Davis Health System, researchers have established that dogs are so far capable of recognizing melanoma as well as bladder, lung, breast and ovarian cancers. We shouldn't therefore be surprised if one day we'll see furry coats along with lab coats in future cancer diagnostic settings.


  • Alexandra Horowitz, "Inside of a Dog, What Dogs See, Smell, and Know," Scribner; September 28, 2010
  • Olfactory System of Highly Trained Dogs Detects Prostate Cancer in Urine Samples, The Journal of Urology, April 2015 Volume 193, Issue 4, Pages 1382–1387

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