Follow the Scent

It’s fair to say I love dogs and I share this opinion with a large percentage of the planet, but as well as their adorableness do you know what makes dogs really impressive? Their incredible sense of smell. Find out how researchers are utilising this in our fight against diseases, even coronavirus.

While we humans rely mostly on our eyes to help us navigate the world, dogs rely not only on their sight but also their sense of smell to assess their surroundings. In fact, dogs dedicate a lot of brain power to interpreting smells, with 100 million sensory receptor sites in their nasal cavity (compared to just 6 million in humans), meaning they devote ~40 times more brain area to smell analysis than humans. Whilst we can smell a teaspoon of sugar in a cup of tea, dogs can smell a spoonful of sugar in two Olympic-sized swimming pools.


Whilst dogs do not speak with their noses, they can decipher a whole story. With a single sniff, a dog’s nose can pick up chemicals produced by objects, whether food, grass, other dogs etc. They can determine if fellow canines are female or male, what they’ve eaten, if they’re related and where they’ve been, to name but a few. Dogs can even move their nostrils independently so they can deduce which direction the scent is coming from. This can be a beneficial “homing” tool for them if they ever get lost. Again, due to the unique combination of chemicals we each produce, dogs are able to tell us apart without even seeing us! Aside from their millions of extra sensory receptors, why is their sense of smell so much better than ours? Dogs have an additional olfactory tool (i.e. organs used to smell) called the Jacobsen’s organ which is specifically adapted to interpret chemical information and is located in the nasal cavity, and opens in the roof of their mouths. Nerves from Jacobsen’s organ can detect chemicals that often have no odour at all, and are lead to the brain where the information is processed. This would be traditionally used by our canine friends to find a potential mate and for pups to find their mother’s milk source. Scientists however have started to utilise this amazing trait for disease detection.


As well as being used as support dogs for the blind, those with autism, epilepsy and other disabilities, researchers hope to use dogs’ amazing sense of smell to detect disease. Medical detection dogs is a charitable organisation, established in 2008, training dogs to identify human disease, working alongside the NHS. These dogs are now regularly used in clinical settings to aid human patients. These dogs are used in two ways: as medical alert dogs or bio-detection dogs. For medical alert dogs, they are trained to detect small changes in an individual’s odour to help alert them to an impending medical event (i.e. a medical emergency), such as severe allergic reactions, people with Addison’s disease, or those with diabetes. In the latter instance, dogs are able to smell hormonal changes in their owners and decipher if they have high or low blood sugar for example.


Bio-detection dogs however are trained to detect disease in the first instance. For example, we can train dogs to detect biochemical changes in a sample (e.g. urine, faecal and skin swabs), and it is likely all diseases have such biochemical changes which would cause odour changes, which dogs could thus detect. (It is said yellow fever smells of raw meat, whilst TB begins with wafts of stale beer and matures to a soggy cardboard smell). The dogs are trained using rewards-based methods and clicker training; when they correctly identify a particular odour, they are rewarded with a treat (be that food, play etc.), much like the training of police drug- or explosives-detection dogs. Their most well known medical use to date is in cancer detection. Depending on the type of cancer, dogs can detect the odour change from skin, breath, urine, faecal and sweat samples. In some instances they can detect these changes in concentrations as low as parts per million! Studies to date have found dogs able to detect colorectal, lung, ovarian, prostate and breast cancers.


Even more interesting to current events, are the dogs helping with research to detect Covid-19 cases. The Medical Detection Dogs charity applied for a UK government grant (of £500,000) to use bio-detection dogs to potentially screen up to 250 potential covid-19 samples per hour! They hope this work will lead to an effective way to better detect the disease earlier on, especially for use at borders, reducing the need for blanket quarantine for everyone arriving in/returning to the UK. Currently this project is collecting samples (e.g. face masks, nylon socks) from frontline workers and patients who haven’t had the virus or could be asymptomatic; this way they will have lots of control samples. There are now 6 dogs in the midst of their training programme, ready for the samples.

There is still a long way to go until we can utilise a dog’s sense of smell to its true potential, but studies to date are promising and dogs are great at working with humans, so there’s that bonus too. The long term aims of medical detection dogs are to provide diagnostic support in cancer cases which are currently difficult to reliably diagnose (such as prostate cancer), and assist with the development of electronic systems for future disease detection (i.e. pinpoint the chemicals which cause the dog’s behavioural change in a sample, so measurement systems can be built to detect the disease instead of a dog). Not only do dogs give us unconditional love and loyalty, they may also one day help us to regularly detect diseases. We do not deserve dogs.

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