When you first think of dogs, what words come to mind? For most of us, our canine companions conjure up images of loyalty, playfulness, or that special knack they have for sensing when we’re upset. But did you know dogs can smell illness? We may joke about them sniffing food in our grocery bags, but they can also detect subtle changes in our bodies that many humans and medical devices cannot.
This superpower is so well-documented that researchers and doctors have used it to train dogs to sniff out a range of medical issues, from cancer to diabetes.
The Incredible Power of a Dog’s Nose
To understand how and why dogs can detect illness, we first need to establish how powerful a dog’s nose really is. Our furry friends have an incredibly sophisticated biological detection system. Dogs’ noses are far more sensitive than ours. The average human nose contains about 5 million olfactory receptors, while a dog’s nose contains up to 300 million. The breeds with the most receptors are often shepherding and hunting dogs bred specifically for scent-detection, such as Beagles, Bloodhounds, Labradors, and Belgian Malinois.
How does this translate to their sense of smell? The more receptors, the more acute the sense of smell. It’s simple math: with 300 million receptors, a dog can detect substances at concentrations as low as 1 part per trillion. Humans, with only 5 million receptors, require concentrations of 100 million parts per trillion to perceive the same scent. This means dogs can detect the faintest chemical compounds that we are completely unaware of.
Smelling the Signs: Dogs Detecting Illness
Here’s the fascinating part: when we become sick, unique chemical compounds appear in the air, on our bodies, and on surfaces around us. Volatile organic compounds, or VOCs, are emitted from many sources, including plants, chemicals, and humans. In the human body, VOCs are produced by the liver, kidneys, intestines, and other organ systems.
A simple example is the smell when you first open a package of plastic wrap or aluminum foil. That odor comes from VOCs released when the material is exposed to air. Similarly, our bodies emit VOCs through metabolic processes. When we become ill—whether from cancer, diabetes, or another condition—our bodies release a chemical signature in the form of VOCs. Dogs can detect these VOCs in our breath, sweat, urine, feces, and other bodily samples. In other words, dogs have a highly specialized biological radar for detecting invisible signals of disease.
Detecting Cancer
A well-known medical application of dogs detecting illness involves cancer detection. Studies over the past few decades have trained dogs to detect different types of cancer, including lung, breast, ovarian, and prostate cancer. A classic 2004 study taught dogs to sniff breath samples from patients, and the dogs correctly identified lung cancer in over 70% of cases.
In another study in the UK, dogs identified bladder cancer in urine samples with around 91% accuracy. This is a remarkable success rate, especially compared to many standard screening tests for cancer, which often have significantly lower sensitivity.
Even more impressive, dogs can often detect cancer in its early stages—before symptoms appear and long before imaging tests reveal it. The implications for diagnostics are huge, making regular cancer screening potentially less invasive and more effective.
Diabetes Alert Dogs and Hypoglycemia Detection
Diabetes is another condition where dogs detecting illness can be life-saving. Many diabetics face dangerous drops in blood sugar levels, known as hypoglycemia. A hypoglycemic event can be fatal if not treated promptly. Dogs trained to detect diabetes sense subtle changes in the scent of their owner’s sweat and breath as the body’s chemical composition changes due to low blood sugar.
Diabetic alert dogs are trained to respond in specific ways, such as nudging their owner, licking their face, or bringing them a glucose monitor. Research shows that some dogs can detect low blood sugar before the person even begins to feel symptoms.
Even untrained pets often behave differently around diabetic owners during hypoglycemic episodes. Many owners report their dogs become restless, hyper-attentive, or clingy when they are sick. While it’s unclear whether they are responding to subtle changes in body odor or behavior, it’s further evidence that dogs have an innate illness-detecting ability.
Seizure Prediction: Dogs That Can Sense the Coming Storm
Dogs have also amazed researchers by predicting neurological events. Seizure alert dogs are trained to recognize subtle signs that precede an epileptic seizure. Some dogs are even trained to detect other neurological conditions, such as migraines or concussions.
The key is that dogs smell something humans cannot. In many cases, seizure alert dogs can warn their owners minutes or even hours before a seizure occurs, giving them time to reach a safe place or take medication.
How Do Dogs Smell a Condition?
You may be wondering, how do dogs detect illness? The short answer is training and patience. To train a dog to detect a particular condition, a sample carrying the scent of that condition is provided. The dog is rewarded when they correctly identify it.
A positive feedback loop is established through praise, treats, or toys when the dog performs correctly. Training requires repetition and patience, but the outcomes are impressive. Dogs have been trained to distinguish between different types of cancer, identify early, middle, and late stages of disease, and detect multiple illnesses simultaneously.
The Bottom Line: Dogs Are Here to Help
It’s important to note that dogs are not a replacement for medical professionals or diagnostic equipment. Instead, did you know dogs can smell illness? is just one example of how dogs can serve as valuable helpers in our lives. A dog alerting a cancer patient to a recurrence, a diabetic to a low blood sugar, or a seizure patient to a pending neurological event can save lives. Trained dogs help detect health conditions earlier, enabling quicker medical intervention.
These findings also inspire technological innovation. Scientists are developing “electronic noses” that mimic the chemical detection abilities of dogs, which could one day be as effective as canine assistance in disease detection.
Even untrained pets often pick up on when their owners are sick. Many pet owners notice that their dogs seem to “know” when they’re unwell. While pets may not communicate it directly, they can sense changes in body chemistry and pheromones, offering a subtle but powerful form of support.
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