Colleen Ferguson of Kent, England, grew concerned when her young German shepherd, Inca, developed a new habit of repeatedly sniffing her mouth. What seemed like a quirk eventually sent Ferguson searching for medical answers — and may have led to life-saving care.
Here's what to know
In 2015, Ferguson spent several weeks noticing a change in Inca's behavior, according to Upworthy. The dog kept zeroing in on her mouth and, Ferguson said, would respond with what looked like a frown.
"Her behavior towards me changed, she just started homing in on my mouth. Every time she could get a sniff of my mouth she would frown," Ferguson told The Mirror. "She just had this focused intent on my mouth, and you couldn't push her away until you had done an outbreath. When she got that she would give me such a look and walk away. In no way did I expect lung cancer at all. It was such a shock because I am a non-smoker, and because I taught biology, I was very anti-smoking."
A full-body scan eventually revealed a golf-ball-sized tumor in Ferguson's lungs. She took that step after a dental visit found nothing wrong and doctors ruled out gut-related issues.
The timing was crucial, as finding the cancer at stage one gave Ferguson a much stronger chance of successful treatment. "The surgeon said … 'that dog saved your life. We never catch it at stage one,'" Ferguson told the BBC.
More background
Researchers have found that dogs can detect illness-related changes in human scent, even though exactly how they do it is still being studied.
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Certain medical conditions can affect the way a person's breath smells. Diabetes is one example, and digestive disorders such as gluten intolerance and celiac disease can also play a role. In Ferguson's case, the underlying cause was lung cancer.
Of course, unusual behavior from a pet does not automatically point to a serious illness. However, it can sometimes be a warning sign.
After the diagnosis, Inca's help continued. Ferguson's dog later became a recovery assistance dog, helping her cope with the anxiety that followed her diagnosis and surgery, Upworthy reported.
What's being done?
Scientists are trying to create technology that mirrors the detection skills dogs like Inca seem to have naturally. Among them is Dr. Andreas Mershin, a physicist who spent nearly 20 years leading MIT's Label Free Research Group before turning that work into a company called RealNose.ai, according to Upworthy.
That effort is focused on an AI-trained "e-nose" built to identify cancer through scent signatures. In May 2026, the device was presented to Queen Camilla, patron of Medical Detection Dogs, at Clarence House.
Researchers are testing the system with donated urine samples that are first assessed by Medical Detection Dogs, then comparing the machine's results with the dogs' findings. The current version targets prostate cancer, with the same method intended to help detect other cancers earlier as well.
"This is a major milestone," Mershin told Medical Detection Dogs. "We've worked to emulate the dogs' abilities and train machines in a similar way, rewarding them for correct identifications. It's like giving our devices a new sense: a nose. Phones already have eyes and ears, but machine olfactors are the next frontier in health technology and AI sensing. This could transform the world of diagnosis, screening, and early detection."
"I was just so lucky. Every day is special with her," Ferguson told The Mirror of Inca. "To catch it at stage one is just remarkable. I don't know how I would have survived with radiotherapy and chemotherapy. She saved me a lot of fuss. It was meant to be."
Where can I learn more?
Inca's alert is one striking example of what dogs can pick up through scent, even outside a formal medical setting. The articles here show that same ability at work in settings ranging from wildlife conservation to invasive species control.
• In Tasmania, handlers found dogs much more accurate than humans at locating harmed wildlife.
• In New Zealand, a possum detector made history with a rare new job after certification.
• A former stray dog, Hera, helps locate wild animals for conservation work.
Canine scent detection is drawing interest in many fields. Researchers want to turn abilities like Inca's into earlier warnings for people and ecosystems alike.
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