Sniffing It Out: Dogs Increasingly Used to Spot Diseases in Humans

They've been our best companions for thousands of years. They've guarded us, protected our property, sniffed out dangerous substances in airports, and helped those of us with limited mobility. But did you know that dogs can also help us stay healthy?
Carmen Valache

Research is increasingly pointing to the fact that dogs can identify conditions like malaria, multiple types of cancer, and even stroke in humans often at such early stages, that sufferers don't even display symptoms yet. And they do so by doing what dogs do best: they literally sniff out diseases.

What's in that snout?

Dogs have an incredible sense of smell. Endowed with as many as 300 million olfactory receptors — to a mere 5 million in humans — dog noses are powerful machines that smell up to 100,000 times better than ours. Their snouts are designed in such a way that the smelling and breathing functions are separate, thanks to a flap that keeps the airflows meant for the two different functions apart. Thanks to this, dogs are able to continue breathing even as they pause to carefully sniff something out.

Dogs also smell separately with each nostril, and then their brain compounds the result — very much like our brains compound the images captured by our eyes into one, holistic picture of reality. This allows dogs to devise a detailed profile of each odor.

And there's more. Dogs also have a special organ in their nose, the vomeronasal organ that helps them identify pheromones, which are hormones that animals give out to communicate with others. This informs them, among others, when to stay off another dog's turf, if another animal is in heat, or if it found food nearby. While all dogs have an acute sense of smell, those with short faces — like pugs — don't fare as well as hunting dogs like greyhounds and dogs with long snouts in general.

Sniffing It Out: Dogs Increasingly Used to Spot Diseases in Humans

Preventive medical assistants

Dogs have proven themselves adept at helping in the early identification of a host of diseases, as repeated studies have shown. It is uncertain exactly what they pick up on, but scientists believe that diseases influence our body odors in ways that are imperceptible to the human nose, but not to the keen canine one. The human body emanates chemicals called volatile organic compounds (VOCs). We routinely excrete thousands of VOCs through our breath and bodily fluids, and they contribute to our signature body odor. When we are sick, our cell metabolism changes, and so do our VOCs. In this manner, dogs can sniff out a host of human ailments, a few of which are listed below.

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In 2018, French researchers teamed up with Medical Mutts, a US-based organization that trains seizure alert dogs, to see how well dogs can detect seizures. Researchers had five dogs sniff out the samples of breath and sweat from different sufferers of epilepsy, some of whom had seizures after the samples were taken. The dogs had been trained to stop if they detected an upcoming seizure. If their guesses were right, they got a treat.

Three of the dogs correctly identified the sufferers that later had seizures 100% of the time. The other two who hadn't had as much training guessed correctly only two-thirds of the time. The findings point to the fact that dogs can be used to improve the quality of life of epileptics and to minimize the risks associated with seizures.


Several studies have shown that trained dogs can successfully spot different forms of cancer in humans. From telling apart sufferers of lung cancer based on their breath to sniffing out ovarian cancer based on blood samples to spotting prostate cancer in urine samples, pups could hold the key to early detection of this often fatal disease.

One particularly interesting study found that dogs trained to detect breast cancer also picked up on lung cancer and melanoma, although they hadn't been taught to do so. This finding could mean that the bodies of cancer sufferers likely emanate a similar substance regardless of the type of cancer that afflicts them.   


Another study involving dirty socks, Gambian schoolchildren and, you guessed it, dogs pointed to the fact that our beloved pets could also hold the key to spotting asymptomatic malaria sufferers. This is particularly relevant since those infected with malaria, even in the early stages when they don't display symptoms yet, emanate a smell that further attracts mosquitoes to bite them.

In the study, two dogs were able to identify up to 90% of the cases of malaria by sniffing out the socks that 175 Gambian schoolchildren wore more than a year and a half prior. What's more, there seem to have been attenuating circumstances for those cases that the pups got wrong. A possible explanation for the confusion, researchers believe, is that infected children had slept in the same bed with uninfected ones, prompting the two dogs to identify six false positives.

A wagging tailed elixir of life

Dog ownership is good for us in general, particularly if we've suffered a stroke or a heart attack. The American Heart Association (AHA) found that people living alone with a dog had a 33% better chance of surviving a heart attack than those living alone. For stroke, the percentage was slightly lower at 27%. In a second study, based on a sample of 3.8 million people, the AHA found that dog owners had a 24% reduced mortality rate compared to non-dog owners and a 31% lower risk of cardiovascular disease and stroke.

Perhaps a side effect of all the love they bring into our lives is that dogs also calm us down, lower our cholesterol, blood pressure and triglyceride levels, and keep our heart rate even when we're under stress.

What more could we possibly ask for in a companion? If I've convinced you to become a dog parent, make sure you adopt one from a shelter though. Besides keeping diseases at bay, shelter pups have extra love to give.

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