It’s been estimated that dogs smell up to 10,000 times better than us. That’s in part because they have about 220 million scent receptors, whereas humans have a mere 5 million. But dogs also inhale in short breaths up to 300 times a minute, meaning that their olfactory cells are constantly picking up new scents. It’s these factors that make them effective – and adorable – real-time disease detectors.
When we’re sick, we produce compounds that waft around us. In infectious or disease states, volatile organic compounds (VOCs) are emitted in breath, blood, sweat and urine, creating a volatilome or ‘aura’ of molecules around the human body. These VOCs often result in changes in body odor, which, studies have found, are detectable by dogs. But what conditions are dogs able to detect?
Here are eight diseases that our furry friends are particularly good at sniffing out.
Research has shown that trained dogs can detect different types of cancer, including melanoma, colorectal (bowel), lung, ovarian, prostate and breast cancers. A 2021 study found that a trained dog could sniff out breast cancer from the urine samples of 200 people with 100% accuracy. Of these people, 40 had breast cancer, 182 had other cancers, and 18 were found not to have cancer.
But dogs don’t necessarily have to be trained to detect cancer. In a 2013 case study, an Alsatian, who happened to be a rescue dog, persistently licked at an asymptomatic lesion behind her 75-year-old owner’s ear. After seeing his doctor, the man was diagnosed with malignant melanoma.
Diabetic alert dogs (DADs) are service dogs that are specially trained to alert their owners to high and low blood sugar levels; both potentially life-threatening conditions. A 2016 study out of the UK suggested that a dropping blood sugar produces a VOC called isoprene, which is not detectable by humans but that dogs can smell. A study published in 2019 looking at the reliability of dogs at detecting blood sugars found that, while there was variability between individual dogs, on average 81% of alerts occurred when sugar levels were ‘out of range,’ that is, too high or too low.
Narcolepsy is a lifelong neurological disorder that affects the brain’s ability to regulate sleep-wake cycles, leaving people prone to sudden attacks of sleep that, depending on when they hit, can be dangerous. In a 2013 study, trained dogs detected 11 out of 12 narcoleptics, leading researchers to conclude that narcolepsy patients produce a distinct dog-detectable odor.
Like narcoleptics, studies have found that people with epilepsy produce a specific odor, discernible by trained dogs, that warns of an impending seizure. Even in patients with different types of epilepsy, which produce different types of seizures, dogs were able to detect ‘seizure odor’ with a sensitivity between 67% and 100%.
Untrained dogs are also capable of detecting seizures. In a 2019 study, 19 untrained dogs of various breeds all displayed a significant increase in attention-seeking behaviors – such as making eye contact with a person – when they detected odors from sweat samples taken from epileptics, compared with samples from non-epileptics. It’s also been suggested that dogs detect seizures by picking up on behavioral, rather than biological, cues. Regardless, the end result is the same.
There are many phases to a migraine, with the first being the premonitory phase, which can present with warning signs like mood changes, food cravings, nausea and brain fog. A lot of the evidence around migraine-detecting dogs is anecdotal, but 53.7% of 1,029 adult migraine sufferers self-reported that their (untrained) dog’s behavior changed prior to or during the initial phase of migraine, with changes usually noticed within two hours before the onset of symptoms. Dog alerting behavior included staring, refusing to leave their owner’s side, sitting or lying on their owner, or herding them to bed or the couch.
A recent Chinese study evaluated the accuracy of sniffer dogs to distinguish between patients with Parkinson’s disease (PD) who were medicated, those with PD who weren’t medicated, and a control group. In people who were medicated, the dogs showed a sensitivity of 91%, for unmedicated PD patients, sensitivity was 89%.
There’s a clinical trial currently running to assess the ability of dogs to discern PD patients from non-PD patients, with a view to using them to ensure early diagnosis of the disease.
Research has found that people infected by malaria produce an odor that makes them more attractive to mosquitoes. In a 2019 study, Gambian children with and without asymptomatic malaria were given socks to wear overnight. After sniffing the socks, two trained dogs were able to correctly identify 70% of children with malaria and 90% of healthy children, even detecting children with low parasite loads.
A just-released review of existing peer-reviewed studies concluded that trained scent dogs are as effective and often more effective at detecting COVID-19 than the tests we currently use, both PCR testing and rapid antigen tests (RATs). And a dog’s ability to detect the SARS-CoV-2 virus is not impeded by the presence of other viruses, such as the common cold or flu.
These studies demonstrate the ability of human’s best friend to be a cheap but quick and accurate means of detecting disease. But despite this, dogs are not widely used for this purpose.
While there has been, of late, a concerted effort to develop technologically advanced (and relatively expensive) biosensors to diagnose disease, perhaps we should instead focus on the dog’s advanced sense of smell. We already use dogs as therapy animals in some hospitals and aged care facilities. Why not put their innate super sniffers to use as disease detectors in these places as well?