6 Medical Conditions That Dogs Can Sniff Out

From cancer to migraines and even seizures, dogs can smell range of diseases.

a brown dog looking up expectantly

Bradley Olson / EyeEm / Getty Images

Dogs are famous for their sense of smell. This sense is so advanced in dogs that they can smell disease or medical conditions. With over 220 million scent receptors—compared to five to 10 million in humans—dogs can smell things that seem unfathomable to us. Dogs’ ability to detect odors is 10,000 to 100,000 times that of humans. They can detect some odors in parts per trillion, and they can detect countless subtleties in scents.

There are dogs who have sniffed out medical issues that even doctors weren't aware of. Dogs can pick up on tiny changes in the human body, from a small shift in our hormones to the release of volatile organic compounds, or VOCs, released by cancer cells. Researchers and dog trainers are just beginning to understand how dogs do this and how we might put them to work in being our helpers in health care. Here are six medical conditions that dogs are able to smell.

Why This Matters to Treehugger

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Perhaps the condition dogs are most famous for detecting is cancer. Dogs have been able to sniff out a variety of types including breast cancer, prostate cancer, bladder cancer, and lung cancer.

There are quite a few stories of a pet dog obsessing about an owner's mole or some part of their body, only to discover in a doctor's appointment that the dog was actually sensing cancer. In one study, a patient’s dog kept licking a mole behind his ear. When the mole was examined, it was confirmed to be a malignant melanoma.

A 2019 study found that dogs can correctly pick out blood samples from people who have cancer with 97% accuracy. Using clicker training with four beagles, lead researcher Heather Junqueira found that the dogs focused their efforts on blood samples from patients with lung cancer, and with one exception, they were highly successful.  The work is part of a larger study of  canine scent detection in non-small-cell lung carcinoma and breast cancer samples.

Five dogs were trained to detect cancer based on breath samples for a 2006 study. Once trained, the dogs were able to detect breast cancer with 88 percent accuracy, and lung cancer with 99 percent accuracy. They were able to do this across all four stages of the diseases.

A trained dog presented with urine samples from patients with cervical cancer, cervical abnormalities, benign uterine disease, and healthy volunteers was able to successfully distinguish the sample of patients with cervical cancer each time.

Study after study has shown that dogs can detect cancer in people, but it may be awhile before your doctor employs a hound for your annual checkup. Researchers still don't know exactly which chemical compounds for different types of cancers the dogs are sensing in these samples to alert to the presence of the disease. This remains a hurdle both for better training of cancer-sniffing dogs and for creating machines that can more accurately detect cancer in the early stages.

How Does the Dog Behave?

The dog's behavior shifts from what might be considered normal. It could paw or sniff repeatedly, and you could have trouble pushing it away. It may nip or lick at lesions, in an attempt to get rid of them for you.


Narcolepsy is a disorder that affects the ability to control sleep-wake cycles. A person with narcolepsy can suddenly fall asleep, even in the middle of a task. It's a dangerous condition as someone who has an attack could be injured falling to the ground or in a car accident if it happens while driving.

Mary McNeight, director of training and behavior for Service Dog Academy, has been training narcolepsy service dogs since 2010. She believes that the dogs are able to pick up on a scent when a narcolepsy attack is coming on. 

In a study published in 2013, Luis Dominguez-Ortega, M.D., Ph.D., found that two trained dogs detected 11 of 12 narcolepsy patients using sweat samples, demonstrating that dogs can detect a distinct scent for the disorder.

How Does the Dog Behave?

A dog trained to detect narcolepsy will warn the owner by barking, nudging, or licking. This indicates the importance of sitting or lying down. The dog may stand over the person's lap when an attack comes on, which prevents them from sliding out of a chair onto the floor; they can also stand over the person to protect them if they are out in public; or they can go get help. Most importantly, they can provide a warning up to five minutes before the onset of an attack, giving their handler a chance to get to a safe place or a safe position.

While large dogs can be helpful in giving a narcoleptic sufferer extra support in balance and mobility after an attack, these dogs don't have to be big to be supportive. It might help to end the episode by licking the owner's face or waking the owner if they sleep through an alarm clock.


For those who suffer migraines, having a warning before one comes on can mean the difference between managing the problem or succumbing to hours or days of intense pain. Fortunately, some dogs have a talent for sniffing out the signs that a migraine is on the way.

A survey of migraine sufferers who owned dogs asked if they noticed a change in their dogs' behavior before or during a migraine. Of the 1,029 participants, 54 percent noted changes in their dog’s behavior either right before or at the onset of the migraine. Behavior differences reported included an increase in attentiveness with the dog sitting on or near the owner and deliberate pawing at the owner. The breeds that owners reported were most likely to alert them to a migraine were mixed breeds, toy breeds, terrier breeds, and sporting breeds. 

It's important to note that the study was conducted with self-reports rather than observation by researchers. Even so, the study shows evidence that many dogs seem to detect and point out a change in their human companion's health.

How Does the Dog Behave?

A dog sensing a migraine about to start could alert you by licking, circling, nudging, staying right by your side, staring at you, pacing, or barking. This could serve as a reminder to take medication that would stave off the worst of the headache.

Low Blood Sugar

Increasingly, dogs are being trained to help people with diabetes by alerting them when their blood sugar level is dropping or spiking. Dogs4Diabetics is one organization that trains and places service dogs with insulin-dependent persons with diabetes. These dogs undergo extensive training to be able to detect and alert their handlers to changes in blood sugar levels.

A 2016 study published in the American Diabetes Association journal Diabetes Care found that dogs detect isoprene, a common natural chemical found in human breath that rises significantly during an episode of low blood sugar. People can't detect the chemical, but the researchers believe that the dogs are particularly sensitive to it and can tell when their owner's breath has high levels of it.

A 2013 study published in PLOS ONE showed that for people with diabetes having an alert dog seems to provide significant improvements in both the safety and quality of life of insulin-dependent persons with diabetes. Positive effects reported by clients with dogs included a decrease in episodes of unconsciousness, fewer paramedic calls, and an increase in independence.

Several theories exist as to how dogs are able to sense hypoglycemia including chemical changes that the dogs are able to smell as well as changes in behavior. There's still uncertainty about whether or not dogs can accurately alert handlers to a blood sugar change at a level beyond chance. A 2016 study of eight dogs that evaluated the reliability of dogs trained to detect and alert for hypoglycemia showed that the animals provided timely alerts 36 percent of the time. A slightly larger study of 27 dogs in 2019 showed an 81 percent rate of alerts when blood sugar levels were out of range. The high degree of variation in the success rate shown in these studies indicates that more research is needed.

How Does the Dog Behave?

A trained dog can wake up or alert an owner whenever blood sugar drops to the level of hypoglycemia, "a condition that can cause shakiness, loss of consciousness, and, if untreated, death." They could do this by jumping up, pawing, or nudging at owner. An untrained dog may show signs of discomfort or anxiety. Retrievers and labradors are often used for detection purposes, since they're quick learners and a good size.


The scientific study of canine response to epileptic seizures is insufficient. While there is anecdotal evidence that some dogs can and do detect the onset of a seizure, most of this has come from small samples and subjective surveys of owners. The level of accuracy and, most importantly, our ability to train dogs to alert a handler to an oncoming seizure remains uncertain.

Scientists don't yet know if there are specific seizure onset cues (such as scent) that dogs can be trained to understand. We can, however, train dogs how to respond to and assist a handler when a seizure occurs. Some service dogs that are placed with seizure patients do develop the ability to detect when a seizure is coming and can provide an alert if the handler pays close attention to the signals the dog provides.

A small 2019 study of five canines found that the dogs were able to differentiate the odor of a patient during an epileptic seizure from the odor of the same patient when they were not experiencing a seizure. Because the study only involved a small handful of dogs and used odor samples that were previously collected, researchers acknowledge that much more extensive testing would need to be done to see if dogs could actually predict seizures before they happened and if other dogs would respond similarly.

In a survey of epilepsy patients in 2003, nine of the 29 patients who had dogs reported that their dogs responded to a seizure. The researchers recognize that while these findings may indicate an innate ability in some dogs to alert or respond to seizures, additional research is needed to learn how to train dogs to be as effective as possible. 

How Does the Dog Behave?

A dog detecting a seizure may bark or paw at their owner, behaving in ways that differ from the norm. Since these could be very subtle cues, the owner would likely need a close bond with the dog to be able to detect the difference. Some dogs are trained to assist the owner during a seizure, but cannot necessarily detect one coming on. These will stay with the owner, standing or lying with them, and sometimes licking their face.

Fear and Stress

The age-old notion that dogs can smell fear is an accurate one. Dogs can smell when we are feeling fear or are experiencing an increased level of stress, even if we aren't showing outward signs. What dogs are smelling is the surge of hormones our bodies release to respond to stressful situations, including adrenaline and cortisol. When dogs smell fear, they show signs of stress. 

White service dog walking next to its handler on a red carpet.

Glynnis Jones / Shutterstock

Thankfully, this can be used to humans' benefit, as dogs can signal a handler that they (or someone else) needs to take a few deep breaths. Dogs that alert handlers of the change in their emotional state—a change that often people aren't even aware they're experiencing—can help prevent panic attacks and other possible episodes associated with post-traumatic stress disorder or other issues.

According to an extensive study of 3.4 million people in Sweden, dog ownership lowers the risk of stress and cardiovascular disease.

We still have a long way to go to discover exactly what dogs are smelling about us, let alone how we can train them to be as accurate as possible about a change in our bodies. Even though many details are not yet known, it's clear that dogs have an uncanny ability to sniff out certain medical issues, and that's a skill that could be a real lifesaver.

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