Dogs Can Detect Parkinson’s Disease by Smell Years Before Symptoms Appear, With Up to 98% Accuracy, a New Study Finds

26 July 2024
by: Juice Juice
in Lifestyle & Wellness

Last updated on

Imagine being able to smell a disease before a single symptom appears, before any medical scan can detect it, before a diagnosis is even considered. Now, imagine your dog doing that for you. Dogs have long been hailed as our loyal companions, protectors, and even emotional anchors. But what if their superpower lies not just in their loyalty, but in their extraordinary noses? With a sense of smell up to 10,000 times more sensitive than ours, dogs can detect a single drop of a substance diluted in enough water to fill 20 Olympic-sized swimming pools. It’s this unparalleled olfactory ability that’s placing them at the front lines of one of medicine’s most difficult challenges: diagnosing Parkinson’s disease early, accurately, and non-invasively. Parkinson’s, a progressive neurological disorder, often lurks in the body for years before revealing its hand. By the time tremors or stiffness appear, vital nerve cells are already significantly damaged. There’s currently no reliable early diagnostic test, and symptoms can be vague or mistaken for aging. But a new study reveals that dogs, trained to sniff out changes in skin secretions, can identify Parkinson’s with up to 98% specificity years before traditional diagnosis is possible. The story behind this discovery is part science, part serendipity, and part human perseverance with a powerful assist from man’s best friend.  

The Parkinson’s Discovery That Started with a Nose

The breakthrough in detecting Parkinson’s disease through scent didn’t begin in a laboratory it began with love, loss, and one woman’s uncanny sense of smell. Joy Milne, a retired nurse from Scotland, noticed something unusual about her husband, Les, long before doctors did. Years before he showed any visible symptoms of Parkinson’s, Joy picked up on a distinct change in his scent an unfamiliar, musky odor that clung to his skin and clothes. At first, she thought it was her imagination. But as time went on and Les was eventually diagnosed with Parkinson’s disease at just 45, Joy’s suspicion took root: what if this new smell was a symptom? Unlike most people, Joy has hyperosmia, a rare condition that gives her an exceptionally heightened sense of smell. Her observation born of daily, intimate contact with a loved one—would later spark an entirely new scientific inquiry. When she mentioned her experience to researchers at a Parkinson’s UK event, it set off a wave of curiosity. Could the disease be detected through body odor? More specifically, could there be a chemical signature in the skin secretions of Parkinson’s patients that dogs or even future diagnostic tools could be trained to identify? Sebum, the oily substance our skin naturally produces, became the focus. People with Parkinson’s often experience changes in skin and sebum production, sometimes years before motor symptoms like tremors or rigidity emerge. These changes, while invisible, emit volatile organic compounds (VOCs) that subtly alter a person’s scent. For someone like Joy or a highly trained dog these olfactory cues stand out. Joy’s experience directly inspired scientists, including Professor Perdita Barran at the University of Manchester, to investigate the link between Parkinson’s and scent. Her anecdotal insight has since helped fuel a growing body of research aimed at developing non-invasive, early-stage diagnostic methods, starting with simple skin swabs.

The Study: Dogs Trained to Detect Parkinson’s

In a double-blind study conducted by the University of Bristol in partnership with Medical Detection Dogs and the University of Manchester, researchers trained two dogs Bumper, a golden retriever, and Peanut, a black Labrador to identify the scent of Parkinson’s disease using nothing more than skin swabs. These swabs, collected from patients’ upper backs, contained sebum, the oily substance produced by the skin that appears to carry a unique chemical signature in people with Parkinson’s. The dogs underwent rigorous training for several months Bumper for 38 weeks, Peanut for 53 using a reward-based system to reinforce correct detection. They were introduced to 205 skin swabs: some from individuals diagnosed with Parkinson’s and others from healthy control subjects. Only when the dogs consistently signaled positive samples and ignored controls were they moved to the testing phase. In the final testing round, the dogs were presented with 100 new, previously unseen swabs 40 from Parkinson’s patients who had been diagnosed but were not yet receiving treatment, and 60 from healthy individuals. This ensured that the dogs weren’t reacting to medication-related changes or recognizing previous samples. The results were nothing short of remarkable:
    • One dog achieved 80% sensitivity (correctly identifying Parkinson’s samples) and 98% specificity (correctly rejecting non-Parkinson’s samples).
    • The other achieved 70% sensitivity and 90% specificity.
These levels of accuracy are well above chance, according to lead author Dr. Nicola Rooney of the University of Bristol, and provide compelling evidence that Parkinson’s has an identifiable olfactory profile. Even more compelling is that the dogs maintained their performance despite the presence of other medical conditions in the participants highlighting the dogs’ ability to zero in on Parkinson’s-specific scent markers. Importantly, while the researchers aren’t proposing dogs as diagnostic tools to replace lab tests, the study does offer powerful proof of concept: disease detection by scent is not only feasible it’s already happening. The goal is to now translate what the dogs can do into scalable technologies, like chemical sensors or electronic “noses”, that could one day screen people in clinics, pharmacies, or even their own homes.

Why Early Detection of Parkinson’s Matters

Parkinson’s disease is often described as a “silent storm.” It begins quietly years before tremors, stiffness, or speech changes appear gradually damaging the brain’s dopamine-producing neurons without outward signs. By the time a diagnosis is made, an estimated 50–70% of those neurons may already be lost, making it harder to slow or manage the disease’s progression. This is what makes early detection so critical. Yet currently, there is no definitive test to diagnose Parkinson’s in its earliest stages. Physicians rely on a combination of clinical evaluations, patient history, and observation of physical symptoms that typically emerge only after significant neurological damage has occurred. Even imaging tools like DAT scans are expensive, not widely available, and are often reserved for confirming rather than detecting the disease. A tool that could identify Parkinson’s years earlier, especially through something as simple and painless as a skin swab, would be a paradigm shift. Earlier diagnosis would open the door to timelier interventions, potentially allowing patients to:
    • Begin therapies that may slow neurodegeneration
    • Make lifestyle adjustments (like exercise or diet) shown to support brain health
    • Participate in clinical trials exploring neuroprotective treatments
    • Plan proactively for care, career, and financial decisions
It also has major implications for research and public health. Detecting the disease in its preclinical phase could help scientists study its earliest biological changes, identify at-risk populations, and ultimately reshape how we approach neurodegenerative conditions. For individuals and families, though, the benefits are more personal. As Claire Guest of Medical Detection Dogs notes, “Timely diagnosis is key, as subsequent treatment could slow down the progression of the disease and reduce the intensity of symptoms.” In other words, the earlier Parkinson’s is identified, the more we can do to maintain quality of life and independence.

How Dogs Smell Disease and What Else They Can Detect

To understand how dogs are able to sniff out Parkinson’s and many other illnesses we first need to appreciate the biological marvel of the canine nose. A dog’s sense of smell is so refined that it can detect some substances at concentrations as low as one part per trillion equivalent to a single drop of liquid in 20 Olympic-sized swimming pools. This olfactory power comes from their 220 million scent receptors, compared to about 5 million in humans, and a highly specialized part of the brain dedicated to processing smells. Dogs also breathe differently than humans: with short, quick sniffs up to 300 times per minute they constantly refresh the airflow to their olfactory system, allowing them to analyze scent molecules in astonishing detail. Their noses even function in stereo, helping them determine the direction of a scent with great accuracy. But what are they actually detecting when it comes to disease? Illnesses often cause subtle shifts in the body’s biochemistry. These changes can affect hormone levels, immune responses, or metabolic processes producing volatile organic compounds (VOCs) that are released through sweat, breath, urine, and skin. Dogs, with their acute sense of smell, are capable of identifying these VOCs long before conventional tests can pick up any abnormality.

Diseases Dogs Are Known to Detect:

    • Cancer: Dogs have been trained to identify several types of cancer including breast, lung, bladder, and skin cancer using breath, urine, or skin samples. One 2006 study found that trained dogs could detect lung cancer with 99% accuracy.
    • Malaria: Dogs were able to correctly identify children infected with malaria 70% of the time just by sniffing socks the children had worn overnight.
    • Diabetes: Diabetic alert dogs can detect isoprene, a chemical that rises in the breath during low blood sugar episodes, and alert their handlers before a crisis occurs.
    • Epilepsy and Narcolepsy: Some dogs have been trained to detect biochemical changes before seizures or narcoleptic episodes occur, often giving minutes of warning that allow people to move to safety.
    • Migraines: Dogs appear to notice a possible spike in serotonin, a chemical that surges before a migraine, which allows them to alert their owners before pain strikes.
    • COVID-19: In several pilot studies, dogs successfully distinguished COVID-19-positive urine or sweat samples from negative ones, sometimes with accuracy comparable to PCR tests.
Each of these abilities highlights how attuned dogs are to the chemical language of our bodies. While science continues to explore exactly which compounds dogs are detecting, there’s little doubt that their noses are picking up what machines often miss.

Dogs, Diagnostics, and Technology

While dogs like Bumper and Peanut have demonstrated impressive accuracy in identifying Parkinson’s through scent, the goal isn’t to fill hospitals with four-legged diagnosticians. Rather, researchers hope to harness what dogs are sensing the precise chemical changes in sebum that signal the presence of the disease and translate it into technological tools that can replicate their detection power. Central to this effort is the search for the specific volatile organic compounds (VOCs) that give Parkinson’s its olfactory signature. Once these chemical markers are isolated, scientists could develop “electronic noses” devices equipped with sensors designed to detect those exact compounds. Such tools could become part of routine screenings in clinics, pharmacies, or even home health kits, much like blood glucose monitors or breathalyzers. The technology isn’t hypothetical. In fields ranging from food safety to explosives detection, artificial olfaction is already in use. The challenge lies in the biological complexity of human scent and the need for pinpoint accuracy, especially in diseases where early diagnosis is both difficult and essential. But the growing body of research including this recent Parkinson’s study is helping to narrow the focus. Still, dogs remain an important part of this journey not just as sniffers, but as biological benchmarks for what machines should aim to achieve. In fact, ongoing trials in the UK and beyond are working to further refine training protocols, understand how variables like breed and personality affect performance, and test dogs across larger and more diverse populations. Not everyone in the medical community is convinced some clinicians remain skeptical of relying on animal detection, and widespread clinical integration will require rigorous validation. Yet the potential is hard to ignore. As Dr. Perdita Barran notes, the simplicity and non-invasiveness of using skin swabs and eventually, scent-detecting tech could radically improve diagnostic accessibility.  

Dogs as Partners in Health

For centuries, dogs have been protectors, guides, and confidants. Now, they’re emerging as something more: potential lifesavers. The discovery that dogs can detect Parkinson’s disease through scent years before symptoms appear is not just a scientific curiosity; it’s a powerful reminder of the intelligence and sensitivity embedded in nature. This research, rooted in a chance observation by Joy Milne and brought to life through the careful training of Bumper and Peanut, opens the door to a future where diagnosis is not only faster and more accurate but also gentler. Not a drop of blood, not a cut to the skin. Just a swab of skin and a nose trained to notice what we cannot. We’re still in the early stages. Larger studies are needed, and the path to clinical adoption may be long and cautious. But the foundations are in place. Whether through trained dogs or sensor-based “e-noses” that mimic them, the possibility of detecting Parkinson’s early before irreversible damage occurs is now more real than ever. What this tells us, beyond the science, is something deeply human: sometimes, the solutions to our most complex problems come from our oldest relationships. In the quiet diligence of a dog sniffing a sample, we are witnessing not just the future of diagnostics, but a renewed partnership between human and animal, instinct and innovation.

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