Dogs have an incredible sense of smell—estimated to be between 10,000 and 100,000 times better than that of humans. This powerful ability has been used for generations to help with hunting, search and rescue, and detecting illegal substances. But in recent years, science has uncovered another amazing skill: dogs can detect certain medical conditions in humans, often before any symptoms appear.
By using their noses, dogs can sense changes in body chemistry, hormone levels, or odors caused by illness or disease. This has led to the development of medical detection dogs, trained specifically to identify and alert their owners or handlers to potential health problems. Here are six medical conditions that dogs have been shown to sniff out, along with how and why they do it.
1. Cancer
One of the most astonishing medical abilities dogs have is detecting cancer. Several studies and reports have shown that dogs can sniff out different types of cancer, including:
- Lung cancer
- Breast cancer
- Bladder cancer
- Prostate cancer
- Colorectal cancer
- Skin cancer (melanoma)
Dogs can detect cancer through breath, urine, skin, sweat, or blood samples. They are able to smell volatile organic compounds (VOCs) chemicals produced by cancer cells and released by the body.
In some cases, pet owners have noticed their dogs acting strangely—such as licking or pawing at a specific part of the body which led to medical testing and a cancer diagnosis. While dogs are not a replacement for traditional screening tools, research is ongoing to develop devices based on canine scent detection.
2. Diabetes (Low or High Blood Sugar)
Dogs can detect changes in blood sugar levels in people with diabetes, often before a person feels any symptoms. These dogs are called diabetic alert dogs (DADs), and they are specially trained to recognize the scent changes that occur when blood sugar is too high (hyperglycemia) or too low (hypoglycemia).
When a person’s blood sugar drops or spikes, their body releases specific chemicals in sweat and breath. A trained dog can pick up on these changes and alert their owner by:
- Pawing at them
- Licking their hands or face
- Barking or whining
- Fetching an emergency kit
Some diabetic alert dogs are even trained to bring a phone or press a medical alert button in case their owner becomes unconscious. For people with type 1 diabetes, these dogs can be life-saving companions.
3. Seizures
Seizure alert dogs and seizure response dogs help people with epilepsy or other seizure disorders. While science is still learning exactly how dogs detect seizures, many people with epilepsy report that their dogs can sense a seizure coming minutes or even hours before it happens.
Trained seizure alert dogs can:
- Warn their owner by barking or nudging
- Help the person lie down safely before the seizure
- Stay by their side to offer comfort and protection
- Retrieve help if needed
Researchers believe dogs may pick up on subtle body changes before a seizure, such as shifts in scent, body movement, or even electrical activity. While not all dogs have this ability naturally, many can be trained to develop it with proper guidance.
4. Migraines
Some migraine sufferers have reported that their dogs seem to know when a headache is coming before they do. Dogs trained to detect migraines use their noses to sense changes in body odor, hormone levels, or behavior.
A person’s body may release different chemicals through their skin or breath before a migraine attack. Some dogs react by:
- Staring intently at their owner
- Nudging or licking
- Whining or acting anxious
- Refusing to leave the person’s side
With training, migraine alert dogs can give their owners a warning, giving them time to take medication or find a quiet place to rest before the pain begins. This early warning system can greatly improve quality of life for those who suffer from chronic migraines.
5. Narcolepsy
Narcolepsy is a sleep disorder that causes sudden and uncontrollable episodes of sleep, often during normal waking hours. People with narcolepsy can suddenly fall asleep while talking, walking, or driving, which can be dangerous.
Dogs trained to detect narcolepsy episodes are known as narcolepsy alert dogs. They can recognize early signs of an attack by detecting chemical or behavioral changes in their owner. When a dog senses an episode is coming, it may:
- Gently nudge or paw the person
- Lead them to a safe place
- Stay close to prevent injury
- Help by fetching a phone or alerting others
These dogs provide an extra layer of safety and peace of mind for people living with narcolepsy.
6. COVID-19 and Other Infections
In recent years, researchers have trained dogs to detect infectious diseases, including COVID-19, with high accuracy. Studies have shown that dogs can identify people infected with the virus even if they are asymptomatic by sniffing samples of sweat, saliva, or breath.
Dogs trained to detect COVID-19 have been used at airports, sports arenas, and hospitals to help screen for the virus quickly and non-invasively. The dogs can sniff out infection in seconds and are surprisingly accurate some studies report over 90% success rates.
Dogs have also shown the ability to detect malaria, tuberculosis, and Clostridium difficile, a bacterial infection that often affects hospital patients.
This area of research is growing, and many scientists believe that medical scent detection dogs could become part of regular disease screening in the future.
Why Are Dogs So Good at This?
Dogs have between 220 million and 300 million scent receptors in their noses, compared to about 5 million in humans. Their brain is also highly specialized to process smell, with a much larger portion devoted to analyzing odors.
Additionally, dogs can detect chemical changes in tiny concentrations, such as parts per trillion. This means they can smell things we could never notice, including tiny changes in body chemistry caused by illness.
It’s not just physical ability—dogs are also highly trainable, loyal, and eager to please. When properly trained, they can learn to alert to specific smells with incredible consistency and reliability.
What Breeds Are Best for Medical Detection?
While all dogs have an excellent sense of smell, certain breeds tend to do better with scent detection work. These include:
- Labrador Retrievers
- German Shepherds
- Golden Retrievers
- Belgian Malinois
- Poodles
- Beagles
- Springer Spaniels
That said, a dog’s individual personality, focus, and temperament matter more than breed. Many medical detection dogs are chosen based on their drive, intelligence, and willingness to work closely with people.
A New Frontier in Medicine
Dogs’ ability to detect medical conditions is opening new doors in medicine and healthcare. With further training and support, medical alert dogs can serve as early warning systems, giving people more time to act and even saving lives.
As scientists continue studying how dogs use their noses, they hope to develop new tools—like electronic “noses” that mimic what dogs can do. But for now, the real-life version remains one of nature’s most powerful diagnostic tools: the loyal and sensitive canine companion.