Parkinson’s disease is notoriously hard to diagnose early. Symptoms like tremors or slowed movement creep in over time, often getting misattributed to aging or other conditions. By the time a diagnosis is made, much of the brain’s dopamine-producing cells are already gone.

This is where doggos can come in.

Bumper, a golden retriever, and Peanut, a black labrador, learned to identify Parkinson’s disease (PD) with uncanny accuracy just by sniffing skin swabs. In a rigorous, double-blind trial, they correctly flagged up to 80% of people with Parkinson’s, while rarely raising a false alarm. In other words, they had a sensitivity of up to 80% and specificity of up to 98%.

Parkinson’s Has a Smell

Parkinson’s doesn’t just affect the brain, it also changes the skin. People with the disease often produce more sebum, the waxy substance secreted by skin glands. And it turns out this sebum carries a unique scent, likely made up of volatile organic compounds (VOCs) altered by the disease’s metabolic fingerprints.

This smell has been reported before by people with hyper-sensitive noses, including a woman named Joy Milne who inspired this entire line of research. Most people don’t have hypersensitive noses. Dogs, on the other hand, have a much keener sense of smell.

Training dogs to detect disease is not new. Medical Detection Dogs has previously trained pups to smell cancers, malaria, and even COVID-19. But Parkinson’s posed a new challenge. The dogs had to tell the difference between swabs taken from people with PD and those from people without, including patients with other neurological conditions.

Over the course of nearly a year, Bumper and Peanut sniffed over 200 samples. The swabs were taken by gently wiping gauze along the upper back and neck — places rich in sebum — from volunteers across 25 UK clinics. Some had Parkinson’s, some didn’t, and nobody (except a computer) knew which was which during testing.

Peanut correctly identified 80% of Parkinson’s cases and falsely flagged just one out of 60 control samples. Bumper performed nearly as well, with a 70% success rate and 90% specificity. Remarkably, the dogs could still detect PD in patients who also had other health conditions, like depression or migraines, underscoring the reliability of the unique Parkinson’s “scent signature.”

Turning This Into a Diagnosis

There’s no blood test or brain scan that can definitively diagnose Parkinson’s early. Most diagnoses today rely on visible symptoms, which appear long after the disease has begun damaging the brain. Researchers say this could help us to truly develop standardized tests to detect the disease.

“Identifying diagnostic biomarkers of Parkinson’s Disease, particularly those that may predict development or help diagnose disease earlier is the subject of much ongoing research,” says Nicola Rooney, Associate Professor at Bristol Veterinary School at the University of Bristol and lead author. “I believe that dogs could help us to develop a quick non-invasive and cost-effective method to identify patients with Parkinson’s disease.”

Claire Guest, Medical Detection Dogs CEO and Chief Scientific Officer, was also happy with the dogs’ performance. She also emphasized that this could

“We are extremely proud to say that once again, dogs can very accurately detect disease. There is currently no early test for Parkinson’s disease and symptoms may start up to 20 years before they become visible and persistent leading to a confirmed diagnosis.

“Timely diagnosis is key as subsequent treatment could slow down the progression of the disease and reduce the intensity of symptoms.”

Another approach is to try and understand what the dogs are smelling. Scientists could isolate the chemical biomarkers in the sebum and develop chemical tests.

For now, the research is still in early stages. Only two dogs made it through the full training pipeline, and the sample size, while impressive for a dog trial, is modest compared to clinical diagnostic standards. But the consistency of results, along with a previous Chinese study that found similar accuracy, suggests that this isn’t a fluke.

As the science catches up to the dogs, one thing is clear: man’s best friend might soon become medicine’s best ally.

The study was published in the Journal of Parkinson’s Disease.