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What Do Dogs Do When They Smell Cancer? 9 Signs to Look for

Written by: Greg Iacono

Last Updated on April 4, 2024 by Dogster Team

girl hugging her pyschiatric service dog

What Do Dogs Do When They Smell Cancer? 9 Signs to Look for

For many years it’s been believed that dogs, thanks to their amazing sense of smell, can detect cancer in humans. In the last few decades, this belief has been confirmed by research showing that dogs can smell certain types of cancer. Today, as with drugs and bombs, dogs are being trained to sniff out cancer and help humans detect it so that they can get their cancer treated before it’s too late.

We’ll discuss the nine signs to look for when a dog smells cancer and other tips and facts about how, why, and when they can detect it.

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The 9 Signs to Look for When a Dog Smells Cancer

1. Persistent Sniffing in One Area of Your Body

One of the reasons humans discovered that dogs could smell cancer was that, when they do, they hone in on the affected area of your body and sniff like crazy. In many cases, when a dog smells cancer, you won’t be able to keep them from sniffing, even by pushing them away, saying “no,” or telling them to stop.

If your dog suddenly starts to sniff you in a specific area of your body and won’t stop no matter how hard you try, it might be time to visit your physician for a checkup.

dog sniffing owner's hands
Image Credit: Prostock-studio, Shutterstock

2. Persistent Licking on One Part of your Body

When dogs are sick, hurt themselves, or have an open wound, one of the first things they do is lick that area to help it heal. Researchers have seen the same behavior when dogs smell cancer in their owners’ bodies. They lick on the specific site constantly, trying to “heal” it the only way they know how.


3. Biting or Nipping on a Certain Part of Your Body

Like licking, a dog will often bite a part of your body where they’ve smelled cancer. By biting the cancerous area, your dog is trying to get rid of the cancer and make you well. It won’t, of course, but dogs will do anything to help their parent.

dog biting owner's foot
Image Credit By: ChutiponL, Shutterstock

4. Staring at You Intently, Sometimes for Hours

Dogs sometimes like to stare off into space, especially if they’re bored. Typically, however, they won’t stare at you for long unless you have something they want, like a bone or a treat. If they smell cancer in your body, your dog might stare at you constantly, day in and day out.

They suspect something is wrong and, researchers believe, stare at you because they’re concerned and don’t know what else to do. Lauren Gauthier, the founder of Magic Mission hound rescue organization, had this very thing happen to her when her dog Victoria couldn’t stop staring at her.


5. Tapping on You With Their Paws

We’ve all had our dogs tap on us when they want something, including when they’re hungry, thirsty, or need to go outside for a potty break. If a dog smells cancer, it will often tap on you incessantly, possibly in a specific area of your body where they smell cancer. This tapping is their way of telling you that something might be wrong, which is a not-so-subtle hint that you should get examined by your doctor.

woman owner and her boxer dog at home
Image Credit: Africa Studio, Shutterstock

6. Snuggling With You Much More Than Usual

Many dogs are snugglers who love to curl up on your lap or lay at your feet. That’s a dog’s way of showing how much they care for their pet parent. If a dog smells cancer, while it might not know what’s wrong, they detect that something is amiss and, in many cases, will snuggle with you far more than usual.

It can be challenging to push your dog away because they’re so concerned. They might also snuggle up to you much closer than they usually do, a possible sign you should get a cancer screening.


7. Whining and Tilting their Head When They Look at You

Many dog owners have wondered what it would be like if their dogs could talk. In a way, they do, usually with whines, growls, and other doggy noises. If a dog smells cancer, it might whine more than usual when it’s around you or stare at you with its head tilted to the side.

It’s your dog’s way of saying, “Hey, I don’t know what’s going on, but something doesn’t seem right.” They might also be upset about something else, but if your dog is whining around you and doing it much more than usual, don’t ignore it.

Pit Bull mixed breed head tilt
Image Credit: Mary Swift, Shutterstock

8. Hiding From Their Pet Parent

While this reaction to smelling cancer might sound odd, researchers believe it’s because your dog fears the problem they’ve detected. Just ask Stephanie Herfel. In 2014 Stephanie’s Siberian Husky, Sierra, was acting very strangely, including hiding in a closet in their home. To make a long story short, Stephanie found out she had cancer, and Sierra was so upset that she hid in fear.

Amazingly, Sierra detected Stephanie’s cancer two more times and noticed it in two other people! Every time, this fantastic dog went and hid in the closet.


9. Hyper-focusing on a Body Area or Part

We’ve seen that dogs will stare, sniff, lick and even nip on a body part where they have smelled cancer. In some cases, they may do all of these things, becoming hyper-focused on a specific area or part of your body in a way they’ve never done before.

They do this because they know something is amiss, and they’re trying to do something about it by alerting you to the problem. At least, that’s what researchers surmise. If you have breast cancer, for example, they may focus on your chest. The same can be said for bladder, prostate, and many other cancers that affect a specific part of your body.

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How Do Dogs Smell Cancer?

It’s well known that dogs have an incredible sense of smell. To give you a better idea, consider that humans have about 6 million olfactory receptors (smell receptors) in our noses, while dogs have approximately 300 million, about 50 times more than we do. Dogs also have a tendency known as neophilia, which means they’re attracted to new and different smells and will investigate them to see what they are. This incredible sense of smell and neophilia help dogs detect cancer. Below are a few other factors that enable dogs to smell cancer.

a dachshund dog looks sick lying on its owner
Image Credit: Leka Sergeeva, Shutterstock

Cancer Has a Specific Smell

When a disease state is affecting your body, the disease has a specific odor or trace signature. Cancer is the same, and when a person has cancer, the odor trace will be detectable to a dog as it’s different from the “normal” smell your body emits.

Several Body Parts and Excretions Can Smell

When a person has cancer, the odor of their disease can be detectable by a dog’s amazing nose. Excretions like sweat, urine, and feces can also have a cancer odor, and dogs can smell it on your breath.

Dogs Can Smell Minuscule Smell Concentrations

Humans have a smelling power ranging from .04 ppm (parts per million) to about 57 ppm. Dogs, however, can smell things in the parts per trillion, which means they can smell a single odor-causing cell in over a trillion non-odorous cells. This incredible sensitivity to smells and odors is why dogs can smell cancer when no human can.

Dogs are Better Than Most Medical Instruments at Detecting Cancer

This fact doesn’t pertain to how dogs smell cancer, per se, but it does prove how well they can do it. Dr. George Pretti, a chemist at the Monell Chemical Senses Center in Philadelphia, PA, has spent almost his entire career isolating the chemicals in cancer that cause it to have a distinct odor. He said this when talking about the canine sense of smell; “I’m not embarrassed to say that a dog is better than my instruments.”

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Which Dog Breeds Smell Cancer the Best?

All dogs have the same powerful smelling ability, but some are better at sniffing out cancer than others, just like some dogs are better at sniffing out drugs and explosives. Today, several breeds are being trained specifically to detect cancer by smell. They include German Shepherds, Beagles, Australian Shepherds, and Belgian Malinois.

That’s not to say that these are the only four dog breeds that can smell cancer, only that they seem to be the best-suited to train for cancer detection. Many of the anecdotal stories we read during the research for this article revolved around other dog breeds that smelled their owner’s cancer, including Siberian Huskies, Treeing Walker Hounds, Labrador Retrievers, and several others.

dog and owner supporting their heads
Image Credit: Anagarcia, Shutterstock

Are Cancer Sniffing Dogs Considered Medically Valuable?

Determining if a person has cancer can involve an invasive and often traumatic array of tests that, in some cases, can cause even more health problems, especially for seniors. That makes a cancer sniffing dog, and the growing advancement of canine cancer detection, invaluable. With a cancer-sniffing dog, detecting cancer is simple, safe, and, most importantly, non-invasive.

Cancer-sniffing dogs can also detect cancer in its early stages, giving the patient time to treat their cancer before it spreads. Moreover, cancer sniffing dogs cause no side effects (aside from a possible allergic reaction), and the tests can be easily performed anywhere, including in a patient’s home.

In short, canine cancer detection and training dogs to detect cancer are incredibly valuable. Because scientists now know that dogs can detect cancer due to smell, they’re developing machines that detect the odor signature of various types of cancer.

Which Cancers Can a Dog Smell?

There seems to be no limit to the types of cancers that dogs can smell, as all cancers have an odor signature they can detect. That being said, there do seem to be some cancers that are easier for dogs to detect than others, including:

  • Colorectal cancer (from feces)
  • Ovarian cancer (from blood samples)
  • Prostate cancer (from urine)
  • Lung cancer (from breath)
  • Breast cancer (from the skin)

How Are Dogs Trained to Detect Cancer?

Although a dog’s powerful sense of smell is something they’re born with, cancer-sniffing dogs are highly trained to detect and respond to cancer. To do this, trainers start training puppies at a young age, around 8 weeks. The training is similar to dogs trained to sniff out bomb-making materials and illegal drugs. Puppies are exposed to the smell repeatedly and then tested to see if they can detect it.

A trainer holds two vials: one with cancer cells and one that’s benign. The puppy sniffs both so that they can get the scent of each. After that, they are exposed to other smells and items with the cancer smell on them and without it. When the puppy detects and reacts to the cancer smell, they’re rewarded with a treat.

From what researchers and trainers have found, the best dogs to detect cancer are those dogs that are very precise in their movements and manners when searching for the smell of cancer. They’re also methodical in searching and are more introverted and aloof than most dogs.

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Final Thoughts

What do dogs do when they smell cancer? They do several things, as we’ve seen today, from incessant sniffing and pawing at you to licking, staring, and, oddly enough, hiding out of fear for your health. All these actions and, admittedly, odd behaviors, spring from the fact that dogs have a powerful sense of smell, and cancer gives off a specific odor they can detect with relative ease. By detecting disease, dogs can help engineers develop machines that identify medical conditions by their unique scent.


Featured Image Credit: Africa Studio, Shutterstock

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