Detecting disease by smell
A new study from Karolinska Institutet show that humans are able to smell sickness in someone whose immune system is highly active. This ability to smell health or disease occurred within just a few hours of exposure to a bacterial endotoxin.
According to the research team behind the current study, published in the journal Psychological Science, there is anecdotal and scientific evidence suggesting that diseases have particular smells. Scrofula, an infection of the lymph nodes, is reported to smell like stale beer, and a person who suffers from diabetes is known to sometimes have a breath smelling of acetone. Research has also shown that dogs are able to smell cancer tumors in the same way as they can detect hidden drugs or missing people.
"However, in this current study we have studied the ability of humans to detect disease by smell", says professor Mats J. Olsson, who led the study. "Being able to detect these smells would represent a critical adaptation that would allow us to avoid potentially dangerous illnesses. The question we asked ourselves in this study was whether such an adaptation might exist already at an early stage of the disease, thereby reflecting a biomarker for illness".
To test this hypothesis, professor Olsson and his team had eight healthy people visit the laboratory to be injected with either a form of lipopolysaccharide (LPS) – a toxin made from bacteria and known to ramp up an immune response – or a saline solution. The volunteers wore tight t-shirts to absorb sweat containing odorant molecules connected to immune response over the course of 4 hours. Importantly, participants injected with LPS did produce a clear immune response, as evidenced by elevated body temperatures and increased levels of a group of immune system signal molecules known as cytokines.
A separate group of 40 participants were instructed to smell the sweat samples. Overall, they rated t-shirts from the LPS group as having a more intense and unpleasant smell than the other t-shirts; they also rated the LPS shirt as having an unhealthier smell. The association between immune activation and smell was accounted for, at least in part, by the level of cytokines present in the LPS-exposed blood. That is, the greater a participant's immune response, the more unpleasant their sweat smelled.
"nterestingly, in a chemical assay the researchers found no difference in the overall amount of odorous compounds between the LPS and control group", comments professors Olsson. "This suggests that there must have been a detectable difference in the composition of those compounds instead."
While the precise chemical compounds have yet to be identified, the fact we give off some kind of aversive signal following shortly after activation of the immune system is an important finding, the researchers argue. The research was supported by the Swedish Research Council, the Bank of Sweden Tercentenary Foundation, the Knut and Alice Wallenberg Foundation, the Osher Center for Integrative Medicine, the Swedish Heart-Lung Foundation, the Center for Allergy Research, the Petrus and Augusta Hedlunds Foundation, the Swedish Asthma and Allergy Foundation, the Stockholm Stress Center, and the Swedish Council for Working Life and Social Research.
The scent of disease: human body odor contains an early chemosensory cue of sickness.
Psychol Sci 2014 Mar;25(3):817-23