The belly button is probably best known as either a source of mystery fluff or the site of 1990s pop stars’ rebellious piercings.
But a new study suggests the navel should be taken more seriously – the particular scent of an individual’s belly button could reveal vital clues to their health.
Researchers analysed the odours captured on swabs that had been swept across people’s nostrils, belly buttons and outer ears.
Those body parts were chosen for testing based on the idea that they might be ‘odour reservoirs’ where deodorants, perfumes and other external chemicals were less likely to interfere with natural scent.
Using laser technology that identified patterns in the odour chemicals allowed them to tell who was in good health, and who had Parkinson’s disease, Covid-19 or mild cognitive impairment.
Samples from the belly button are a good source of body odour chemicals because they are ‘not disturbed by soap too often’, says lead researcher Dr Thorsten Graunke, an expert in digital sensory perception from the Fraunhofer Institute for Integrated Circuits in Germany – who suggested the study could pave the way for a kind of ‘rough’ at-home screening for various illnesses.
Each of us is surrounded by a unique and invisible cloud of chemical gases, called volatile organic compounds, or VOCs.
‘The human body constantly sheds VOCs through normal metabolic processes,’ explains Dr Graunke. ‘Every time we exhale, sweat or shed microscopic skin cells, we release a unique cloud of these chemicals – collectively known as the human volatilome.’
Samples from the belly button are a good source of body odour chemicals because they are ‘not disturbed by soap too often’
The volatilome can change when someone has a disease or an infection. Stories of pets sensing an owner’s cancer before they had even noticed symptoms themselves are probably due to the animals’ more sensitive noses picking up on those changes, scientists say.
The new study, published in Scientific Reports, attempted to sample the volatilome by swabbing participants’ nostrils, belly button and the ear’s concha (just behind the opening of the ear canal).
Six participants were in good health, while six others were known to have Parkinson’s, Covid-19 or mild cognitive impairment. They focused on those conditions because earlier research found links with changes in body odours.
Each site was swabbed for around ten seconds. Then the swabs were put into sealed, Ziplock bags and frozen at -20C (-4F) to preserve the compounds. The samples were then tested with laser-based photoacoustic spectroscopy, which involves shining light of different wavelengths on the gases, which vibrate in response. Different chemicals create vibrations that give a distinct pattern.
The researchers were able to identify which illnesses participants had based on those patterns – with the clearest signals coming from nose and belly button swabs.
They also found the most important information could be captured using only a handful of wavelengths, which ‘could speed up measurements in future and simplify the setup,’ says Dr Graunke.
The swabs from the healthy controls and people with Parkinson’s disease or cognitive impairment were taken in an odourless hospital room. For infection-control reasons, the Covid patients took the samples themselves.
Does that suggest that one day, people could take the samples themselves at home? ‘Possibly!’ says Dr Graunke. ‘These swabs could be used as rough screening.
‘Our vision is to build a handheld device where swabs can be inserted,’ he says, while stressing that is ‘a long-term vision, not currently within reach’. This was only a small pilot study, he adds – the team is seeking funding to use the method in a larger group.
Professor James Logan, an olfactory science expert and founder of Digital Odour Technologies, a spin-out from London School of Hygiene and Tropical Medicine, says: ‘I’m always excited to see studies like this because the more we can understand odour and use different methods to try and figure out what’s going on there, then the better we can use it.’
His company has developed a handheld device to detect VOCs in odours to spot if a patient has dengue or malaria.
In medicine, the main advantage of odour detection over traditional samples such as blood or saliva is that it is non-invasive, says Professor Logan.
‘Odour also tends to change at a very early stage of infection,’ he adds. Dogs trained to smell Covid-19 can detect the disease earlier than lateral flow tests.
The use of odour as a diagnostic tool is in its infancy, but examples include medical detection dogs that can detect imminent seizures, or dangerous swings in blood sugar levels in those with diabetes.
‘With the sector moving at pace, I think this will change soon and we will start to see machines that can smell and tell us when we are ill,’ says Professor Logan. ‘One day it will be as small as a smartwatch.’
A growing body of research suggests every disease will have a distinct odour, down to a very specific level, he says. ‘Some studies have shown you can tell the difference between two different types of the flu, for example.’
Belly button sampling makes sense, he adds. ‘Previous studies have looked at the armpits, because they tend to be very smelly. But people use deodorant, and the chemical compounds in the deodorant mask the disease-linked VOCs. Even when you stop using it for a while, there’ll still be remnants of the deodorant, and that can interfere with testing.
‘So somewhere around the abdomen area is quite good, because it’s less likely to be contaminated with other things.’
