Belly button odor may contain more information about health status than previously thought. A preliminary study found that chemical profiles collected from samples in this area could differ between healthy individuals and those suffering from Parkinson's disease, mild cognitive impairment, or COVID-19.
This study was conducted as a conceptual check and included only 24 participants, so the results obtained do not yet allow us to claim that the belly button can be used for disease diagnosis.
The belly button area naturally serves as a reservoir for dead skin cells, sebum, and sweat, and is also a habitat for bacteria that feed on this material. The combination of these elements forms compounds responsible for the characteristic odor of this area.
These compounds belong to the class of volatile organic compounds (VOCs)—small carbon-containing molecules that easily evaporate upon contact with air. They can leave the body through sweat, breath, urine, saliva, and oils produced by the skin.
The composition of these compounds can vary depending on various factors, such as diet and medications taken. Furthermore, diseases can alter the chemical composition of odors produced by the body.
In the laboratory, researchers placed cotton swabs on a specially designed stand and directed highly purified synthetic air onto them. This process allowed the transfer of volatile organic compounds into a laser-based photoacoustic spectrometer.
When VOCs absorb infrared light emitted by the laser, the absorbed energy heats the gas around the molecules. This causes an expansion that generates small pressure waves, similar to sounds that can be detected by an extremely sensitive sensor.
Since different molecules absorb infrared light with varying intensity at specific wavelengths, researchers were able to create a kind of spectral 'fingerprint' of the chemical mixture in each sample.
Subsequently, a statistical method known as principal component analysis was applied to identify patterns and check whether samples from people with the same condition exhibit similar characteristics.
Identified differences in chemical composition
The most obvious differences were observed in samples from the nose and the belly button. Regarding the belly button, the chemical profiles showed distinct patterns between different groups. The greatest separation was observed between healthy participants and those with mild cognitive impairment.
Samples from people with Parkinson's disease and COVID-19 were among these groups, albeit with some overlap in patterns.
Researchers also checked whether one of the patterns persists over time. Samples were collected from three other Parkinson's patients two weeks after the initial measurements. When this new data was included in the analysis, it grouped together with the initial samples of Parkinson's patients.
However, scientists emphasize that the result is preliminary because only three participants were added. Nevertheless, the concentration of new samples in the same group suggests that the observed pattern may not just be a feature of specific individuals on a particular day.
Moreover, the experiment showed that simpler equipment might be sufficient to identify patterns.
In the initial stage of the study, scientists analyzed a wide range of infrared wavelengths. When searching for the most useful wavelengths for separating groups, it turned out that only five individual wavelengths could separate the groups almost as effectively as the most informative spectral range.
This means that future devices could be smaller, simpler, and potentially cheaper than the full system used in the experiment.
Limitations of the study
Despite the findings, researchers point out significant limitations. The first is the limited number of participants. With only 24 people, the study serves only as a conceptual check and does not allow a conclusion about using the belly button for diagnosing health problems.
The age of the participants is also an important issue. Researchers noted that age correlated with differences in spectral fingerprints. Moreover, in the small analyzed group, age and diagnosis were very closely linked, which hindered the complete separation of the influence of each of these factors.
With a larger sample size, it would be possible to study whether disease-related patterns persist independently of aging.
Another point is that the experiment was conducted under strictly controlled laboratory conditions. In real life, factors such as soap, perfume, personal hygiene, and environmental pollutants can change the chemical composition of samples.
Therefore, to confirm that the observed patterns are truly related to diseases, larger studies with age-controlled groups and conducted in conditions closer to daily life are necessary.
For now, researchers view these results as an indication that compounds present in body odor may represent a potential area for studying non-invasive methods of disease detection.