Can Dogs Smell Cancer: A Closer Look at What the Dog Nose Knows

By Chelsea Hunt-Rivera / April 30, 2018

That a dog’s sense of smell vastly exceeds that of a human being’s is general knowledge. But not everyone knows much about what the limitations of a dog’s nose are. Dogs can be trained to alert us to the presence of narcotic drugs and explosives. They can track the scent of missing people. They can even smell the dipping blood sugar levels of a diabetic. The big question now, is: can dogs smell cancer?

If you want a short answer, then yes, absolutely. Dogs can smell cancer. But the longer answer is far more interesting. Dogs are phenomenal creatures. They guard us, they guide us, and now, they are warning us of an illness long before any lab test or screening process would.

Can Dogs Smell Cancer in Humans?

dogs can smell illnesses in humans

So, we’ve established that dogs can smell cancer. Naturally the next step for anyone interested in the topic would be to ask “How” dogs smell cancer.

Humans and dogs have been evolving alongside one another for hundreds of thousands of years. The amazing bond we have with our canine companions today comes from a codependency which formed between the first domesticated dogs and their humans. People and dogs needed each other to survive.

With their sophisticated sense of smell, dogs could pick out weak and ill animals. A sick animal is far easier to take down than a healthy one. Dogs can smell illnesses in humans because it is a product of their evolutionary process as predators.

Domesticated dogs today don’t need to use their noses to pick out weak prey. They use their noses to detect illnesses and weaknesses in their humans as a form of self-preservation. As their primary caregivers, if something is wrong with us, it may affect our ability to shelter and feed them.

How Does That Cute Button Nose Work?

Dogs rely on their sense of smell to navigate the world. They have an Olfactory Cortex that is around 40 times bigger than that of humans. Humans don’t need one that big because they primarily use vision (i.e. their Visual Cortex) to navigate the world. Where humans have maybe 5 million smell sensitive receptors, dogs have up to 300 million. They even have an added olfactory organ called a “Jacobson’s Organ”. It’s a sort of second nose that exists purely to improve a dog’s sense of smell.

It is said that a dog can smell parts per trillion. TRILLION. Most people can’t even differentiate between 3 different types of smelly cheese!

How Dogs Detect Cancer

Cancer cells give off a sort of waste substance. This substance consists of volatile organic compounds that have a specific scent. Some Oncologists say that they can smell that scent in the exhaled breath of patients who are suffering from stage 3 or 4 cancer. So yes, people can apparently smell cancer too. However, dogs are able to detect cancer in people from stage zero.

There are many stories of dogs making their owners aware that they have cancer. One example is of a dog whose behavior suddenly changed for no apparent reason. The dog became depressed and persistently sniffed at its owner’s breast. The owner had breast cancer tests done and the results came back negative. It was only after she went for a biopsy that they discovered the lump in her breast was cancerous. She had breast cancer. It was stage zero. The best of the early stages really, when it comes to a detection time frame. Dogs can single-nosedly redefine the parameters of the Five-Year Survival Rate.

how dogs detect cancer

Another example is of a dog who would not stop sniffing at a mole on its owner’s leg. Turns out, it was not a benign mole, but a malignant melanoma.

Dogs have the ability to smell the organic compounds given off by tumorous cells on the skin (skin cancer), in breath (lung cancer) in urine samples (prostate cancer) and more. A dog can be as good if not better at detecting cancer in samples than a prostate-specific antigen (PSA) Test.

Trained dogs, like medical detection dogs, learn to signal to their handlers when they can smell cancer in samples or patients by positive reinforcement. Some sniffer dogs have even been trained to differentiate between various types of cancer. A dog can tell the difference between a prostate specific antigen (PSA) or antigens in other organs. A dog could detect lung cancer in patients before the x-ray of their lungs load show up on a screen.

The Types of Cancer Dogs Can Detect

Here are some of the types of cancer which our four-legged super sniffers have detected in humans:

  • Bowel cancer
  • Bladder cancer
  • Breast cancer
  • Cervical cancer
  • Endometrial cancer
  • Lung cancer
  • Ovarian cancer
  • Prostate cancer
  • Skin cancer

Can All Dogs Detect Cancer?

There are certainly breeds that have a superior sense of smell, but that is not to say that only certain breeds are good at scent detection. It usually comes down to the individual. Many a Guide Pup in training has failed their classes because they constantly get distracted by odors and go off on sniffing sprees. Those are the dogs that need to go to Scent Pup School.

Most dogs who show an interest in sniffing all the glorious scents in the world around them can be trained to detect specific odors and alert their owners to these smells. But an untrained dog may very well smell cancer, and not be particularly interested in it. Even if they were interested, they may not think that we are interested, and won’t even try to communicate it to us.

Then there are the cases in which dogs try to warn their owners, but people tend to not always pay close attention to what their dogs are trying to tell them.

Gifted Breeds: Which Dogs Make the Best Sniffers?

dogs that are the best sniffers

Dogs can smell up to 100 000 times better than we do. So, let us not think certain breeds inferior because their sense of smell is not “phenomenal”. They still smell a whole lot more than we do.

There are however definitely breeds that are known to produce scent dogs with astounding sniffing skills.

  • Basset Hounds
  • Beagles
  • Belgian Malinois
  • Bloodhounds
  • Coonhound
  • German Shepherds
  • English Springer Spaniel
  • Labrador Retrievers
  • Pointers
  • Portuguese Water Dogs

Why Cancer Detection Dogs Aren’t in Every Hospital

It takes a lot of time, energy and resources to train a single dog to identify cancer in patients. The few dogs that are trained and used in studies to detect the presence of cancer, work on a small scale. They get 8 urine samples and have to detect which of the samples has the cancer. Once they detect it, they get a reward. A handler can reward a dog for identifying a sample or person with cancerous cells, but what if nobody knows whether or not there is cancer to be detected? You cannot reward a dog when you aren’t 100% sure that the dog is right.

What if a dog smells 100 patients, and not one of them has cancer? The dog may lose interest or confidence when they do their job and there is no reward. They are trained to detect cancer, not the lack thereof.

Dogs are not machines. Like people, they have bad days and sometimes they simply don’t feel like working. Using the word “unreliable” seems unkind, but in a world where time is money, and value is based purely on productivity and results, using dogs would inevitably be labelled “inefficient”.

Dog vs. Machines: How Dogs Are Helping to Revolutionize Illness Detection

dog with cancer patient

Dogs may not be the future standard detectors of cancer and other illnesses. It’s simply not a feasible option. What they are doing, is helping researchers work on creating an Electronic Nose. These “E-Noses” are similar to Gas Chromatography – Mass Spectrometry instruments (used to detect anything from explosives to narcotics). E-noses will operate in a less forensic realm. They are designed to detect the presence of illnesses such as cancer, in a low-cost and non-invasive manner.

Dogs help researchers identify the different kinds of volatile organic compounds found in cancer patients. Once a compound has been identified, researchers need to get the detectors of the E-Nose to detect that specific compound.

What makes dogs and their noses so special, is that they can smell cancer and tumors at their inception. E-Noses need to be able to do the same. They could be an affordable and accessible standard screening test for the early detection of cancer.

As cool as the science is, no machine will ever replace the need for our dogs or their noses!


Can dogs actually sniff out cancer in humans?

Can my dog detect illnesses too?

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About the author

Chelsea Hunt-Rivera

Chelsea Rivera is a Dedicated Pet Parent who loves to create amazing content for pet owners and is helping change pet wellness as the Head of Content for