Is sweat from a different cause 鈥� such as exercise, anxiety or illness 鈥� chemically unique? Can dogs tell the difference?
Claire Guest,
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Medical Detection Dogs, Milton Keynes, UK
In short, yes. Sweat is mostly composed of water, but it also plays a role in the excretion of toxins and waste products from the body.
These substances can be hormones, minerals or volatile organic compounds (VOCs) produced as a . They can vary from person to person and depend on the cause of perspiration.
For dogs, which possess up to 300 million olfactory receptors, sniffing out the difference can be easy once they are trained to detect a specific scent. For instance, in a 2022 study by researchers at Queen鈥檚 University, Belfast, and Newcastle University, both in the UK, samples taken from participants before and after completing a stressful mental arithmetic task. This suggests that we produce different odours when we are stressed than we do when relaxed.
For those of us at , these findings came as no surprise. In our 15 years of training dogs to detect disease, we have used skin swabs or sweat samples in projects such as the detection of Parkinson鈥檚 disease, malaria and , even when asymptomatic.
The dogs can pick up on subtle changes and .
We also use sweat samples to train medical alert assistance dogs for clients with health conditions such as postural orthostatic tachycardia syndrome and Addison鈥檚 disease.
Interestingly, while disease-specific VOC patterns have been identified for some conditions, the .
However, further research that combines canine olfaction with chemical profiling could help further our understanding of how dogs differentiate between the chemical 鈥渇ingerprints鈥� left by changes in hormone production or our microbiome, and also help improve the early detection of disease.
Joy Milne,
super-smeller Perth, UK
I am fortunate (or unfortunate, depending on how you look at it) to have a very sensitive sense of smell.
In my experience, the smell of sweat resulting from vigorous exercise is quite different from that of sweat from a different cause, especially if someone is ill. I think the variation is due to different volatile chemicals in the sweat.
For me, the sweat from exercise where you get really out of breath has a distinctive salty smell to it. I can also tell the difference between people of different sexes and age groups. Sweat from men and women, older and younger people, each has a distinct smell.
I don鈥� t have much experience of the smell of sweat from anxiety, so I couldn鈥檛 comment on whether this has a distinct odour.
When I was a nurse, patients were often anxious, but that was usually linked to an illness they had, such as heart disease or diabetes. It wasn鈥檛 pure anxiety alone.
The sweat of people with a very high temperature has a distinct chemical smell, due to their infection. When the person is getting better, the smell reduces.
To me, covid-19 and flu have distinct smells, and there are also differences depending on whether someone has a viral or bacterial infection. Everything produces different volatiles.
[To read about how Joy Milne鈥檚 incredible sense of smell is being used to develop a new diagnostic test for Parkinson鈥檚 disease, go to newscientist.com/article/mg24132200-300-meet-the-super-smeller-who-can-diagnose-parkinsons-at-a-sniff/]
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