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Can Dogs Smell Diseases like Cancer in Humans?

Written by Anna Hollisey

Updated

Golden Retriever nose close up

Dogs aren’t just awesome companions. They’re scientifically awesome, too! Like some other animals, dogs are now known to have the ability to sniff out certain diseases. Their sense of smell is between 10,000 and 100,000 greater than a human’s. In the future, could our dogs become early-detector systems for diseases like cancer? Read about some of the ground-breaking research here. 

The Lancet Legend

The idea that dogs can detect cancer emerged in 1989. Hywel Williams and Andres Pembroke, consultants at Kings College London, wrote to The Lancet journal to report a case in which a dog had been sniffing and biting at a lesion on his owner’s back. She attended the doctor and found it was a malignant tumor.

Since then, others have reported that their dogs have alerted them to cases of cancer by behaving strangely. Could it be true? Tumors produce compounds which could be detected by dogs’ amazing sense of smell, according to a team of US researchers (in a paper published in 1999). 

Evidence that Dogs Can Detect Cancer

In 2004, a UK study reported that a panel of 36 dogs had detected cancer by sniffing urine, with a success rate of 41%. 

These dogs were trained to detect bladder cancer over a period of seven months. The team chose a random panel of dogs, rather than trained scent hounds. They used urine samples and search-and-find scent games to teach the dogs to identify the urine from people diagnosed with cancer. The dogs performed well in tests, identifying the cancer patient in 41% of cases, “providing convincing evidence that dogs do, indeed, have this ability”.

In 2014, an Italian research team trained a pair of female German Shepherd dogs to detect prostate cancer in urine samples. They tested with 900 samples and the dogs identified 97% correctly, which is extremely significant. 

Another team in Spain worked with a Labrador-Pitbull cross who was trained to identify the presence of lung cancer using exhaled air. Their tests showed another amazing result: the dog was correct in more than 95% of cases. They commented that there is potential for medical teams to use dogs to improve early detection of lung cancer, which can then be treated more effectively. 

Do cancer cells have a unique odor or scent pattern? A research team in Israel theorized that they do, and tested dogs – who were trained to detect breast cancer – using samples from patients with melanoma or lung cancer. They reported that their two trained dogs identified 100% of the cancer cell cultures. In their research paper, the authors said: “These [pre-existing] studies, taken together with the results of the present study, provide definitive proof […] that dogs can detect different types of cancer by sniffing the volatile elements secreted by the tumor cells.”

Dogs Are Supporting People with Diabetes

Dogs are known to help their owners when blood sugars are low or high. Diabetic Alert Dogs (DADs) are widely used and have been trained to support diabetic people ever since some of them started doing it instinctively. While dogs are less likely to check their owners when they’re asleep, they bring other advantages – owners worry less and benefit from better quality of life in general. 

Dogs Are Helping to Eliminate Malaria

In another research project funded by Bill and Melinda Gates, children in Gambia were asked to wear socks overnight; these were then passed over to trained scent dogs. The samples from children who had malaria (without symptoms) were correctly identified 70% of the time. 

Research leader Steven Lindsay explained that malaria is often carried by people who don’t display symptoms, but dogs can recognize the odor produced by malaria parasites. They could become an important part of the initiatives to eliminate malaria in countries around the world. 

Can Dogs Detect COVID-19?

In an interview with NATURE magazine, veterinarian Cynthia Otto explains how her team used samples of sweat to train dogs to recognize COVID-19 in humans. “They could do it — dogs can definitely detect the disease,” she confirmed. But she also pointed out the margin for error which comes from using our canine assistants. “Dogs that work well in the laboratory don’t always work well in a community environment.” Out in the wild, asked to sniff people standing in a line, with competing smells coming from everywhere, dogs did not perform as well. Dogs, added Cynthia, have bad days and good days like we do!

Will Dogs Work in Medical Centers in the Future?

Unfortunately, writes Jonathan Jarry for McGill, “there are too many obstacles to clear before we release Fido in the laboratory”. Some people are afraid of dogs, and trained scent hounds tend to have shorter shift hours than our typical doctors. Plus, these dogs must be regularly assessed to ensure that they are performing at a high level of accuracy. The number of dogs and trainers who would be needed makes it difficult and impractical to roll out. 

So… for all these reasons, we might not find dogs working alongside doctors at our clinics. But we know that samples can be collected and frozen or transported to testing zones: dogs have been able to identify expired air as well as previously-frozen urine. 

Alternatively, the future may be developing machines which recognize patterns in scent, just like a dog does.

In 2021, a team at MIT reported that they’d been working on an olfactory device which uses AI to ‘learn’ to distinguish between diseased and healthy breath samples. Lead researcher Andreas Merchin said that one day, every phone could have this device built into it. But right now the machine, despite being 200x more sensitive than a dog’s nose, is “100% dumber” than a dog. Mershin became involved with the new project after witnessing a dog persistently identifying a healthy patient in a bladder cancer trial. Months later, the patient was found to have the disease – proving the researchers wrong, and the dog right. And if that isn’t another good reason to keep our beloved canines close, we’ll be darned!