Disease stinks – the link between smell and disease

By Charlotte Gillespie

When I was looking up an image for a ‘sick person’ for this blog, the results are more or less all the same. A person in bed, with a cold compress on their head, a thermometer hanging out of their mouth and a very sorry expression on their face (which is sometimes green, depending on the artists’ creative license). This represents the general symptoms we would expect to see in someone who was ill. These visual cues are often used in the field of diagnostics. However, research is starting to show that a different sense could be exploited in order to diagnose patients. Smell.

Joy Milne – the super smeller

There have been limited cases in which a human has diagnosed someone based purely off scent. Modern doctors are more likely to give you a blood test than a whiff! However, one woman, Joy Milne, realised she could smell Parkinson’s when she went to a Parkinson’s support meeting and that everyone in the room with the disease smelled like her husband, who had been diagnosed a few years before. After asking some doctors about her revelation, they tested her theory by giving her a set of T-shirts. Some had been worn by Parkinson’s sufferers, and some were controls. After being asked which ones had been worn by people with the disease, she labelled all but one correctly, with only one control being identified as having Parkinson’s. As if this accuracy wasn’t high enough, a few months later, this control was diagnosed with Parkinson’s, meaning she had correctly identified the disease status of every single sample.

Why does disease smell?

Since then, research exploring this link between smell and disease has grown dramatically. Researchers have suggested the reason for this change in smell after contracting an illness is due to odorous volatile organic compounds (VOCs), which the human body naturally releases as a product of metabolic processes. As disease can change these metabolic processes, it stands to reason that the VOCs being released by the body would also change, resulting in a shift in smell. Being able to identify how smell changes for individual diseases could mean the development of non-invasive tests that could help diagnose disease before the presence of other symptoms, much like Joy was able to do in the T-shirt study!

A man’s best friend

One animal which may be better equipped to smell disease, is the dog.  Dogs have a better sense of smell than humans and are able to sense molecules at one part per trillion, which is the equivalent of sensing a singular drop of water in 20 Olympic sized swimming pools. This is due to small projections called turbinates inside their nasal cavity which increases its surface area. So far, research has been promising for dogs being able to detect cancer samples amongst controls, as shown in the image (I will admit, the first time I saw this image I wondered about the legitimacy of results considering the sample was labelled. Then I remembered that dogs can’t read). Therefore, this research provides promise for using dogs in cancer diagnosis. The US president himself said a few weeks ago that dogs ‘could help cure cancer’. A slight overestimation by Joe Biden but the thought was there.

However, introducing disease detection dogs to clinical settings is debated. Being sniffed and then barked at by a cancer detection dog on a Wednesday morning at a general check-up may be slightly unnerving to some individuals . On top of this, dogs are only human (!) and have bad days like the rest of us, which could result in inaccuracies, something to be avoided at all costs in the field of diagnostics.

The eNose : The Future of Diagnostics?

Therefore, researchers have started to look into the Electronic Nose, an arrayed sensor technology which creates a VOC profile of the sample, much like a dog or humans olfactory system does. This VOC profile could then tell doctors whether this person is indicating a certain disease. If this technology is perfected, it could be rolled out on a nationwide basis in screening programmes, leading to earlier diagnosis of cancer and other diseases which affect much of the population. Therefore, this link between smell and disease, which initially seemed questionable, could save lives.  

Additional Reading

Ehmann, R., Boedeker, E., Friedrich, U., Sagert, J., Dippon, J., Friedel, G. and Walles, T., 2011. Canine scent detection in the diagnosis of lung cancer: revisiting a puzzling phenomenon. European Respiratory Journal, 39(3), pp.669-676.

Jenkins, E., DeChant, M. and Perry, E., 2018. When the Nose Doesn’t Know: Canine Olfactory

Function Associated With Health, Management, and Potential Links to Microbiota. Frontiers inVeterinary Science, 5.

Rozenbaum, M., 2020. The Science Of Sniffs: Disease Smelling Dogs | Understanding Animal Research | Understanding Animal Research. [online] Understanding Animal Research.

Available at: <https://www.understandinganimalresearch.org.uk/news/research-medical-benefits/the-science-of-sniffs-disease-smelling-dogs/#&gt; [Accessed 3 November 2020].

Shirasu, M. and Touhara, K., 2011. The scent of disease: volatile organic compounds of the human body related to disease and disorder. Journal of Biochemistry, 150(3), pp.257-266.

Sonoda, H., Kohnoe, S., Yamazato, T., Satoh, Y., Morizono, G., Shikata, K., Morita, M., Watanabe, A.,Morita, M., Kakeji, Y., Inoue, F. and Maehara, Y., 2011. Colorectal cancer screening with odourmaterial by canine scent detection. Gut, 60(6), pp.814-819.

Walker, D., Walker, J., Cavnar, P., Taylor, J., Pickel, D., Hall, S. and Suarez, J., 2006. Naturalistic quantification of canine olfactory sensitivity. Applied Animal Behaviour Science, 97(2-4), pp.241-254.

About the author:

Charlotte Gillespie is a fourth year Biological Sciences student at the University of Birmingham. She loves biology and whipping out the occasional scientific fact on her group chats. If you want to find out more about her work you can follow her on Instagram @charlottegillespie_

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