A new way of detecting sickness might be literally right under our noses. A study published in Psychological Science suggests that humans are able to smell sickness in someone whose immune system is highly active within hours of exposure to a toxin.

During the study, 8 healthy individuals were injected with either lipopolysaccharide (LPS), a bacterial toxin that produces a strong immune response, or with salt water. The participants wore tight t-shirts that absorbed sweat over the course of 4 hours, and those who were injected with LPS produced an elevated immune response as expected. The researches collected the shirts, cut out the armpits and put the fabric into bottles. A separate group of 40 volunteers were then asked to smell the sweat samples and rate their odor based on intensity and unpleasantness. Overall, they rated the samples from the LPS group as more unpleasant, intense, and generally as having an unhealthier smell than the shirts from the control group.

The relationship between immune activation and smell was accounted for partly by the level of cytokines present in the LPS-exposed blood. The greater a participant’s immune response, the more unpleasant their sweat smelled.

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Anecdotal and scientific evidence even suggests that different diseases have different smells. For example, people with diabetes are reported to have breath that smells like rotten apples or acetone. Those with yellow fever have been said to smell like a butcher’s shop and people with the lymph node infection scrofula smell like stale beer.

However, in a chemical assay, the researchers found no difference in the overall amount of odorous compounds between the LPS group and the controls. “This suggests that there must have been a detectable difference in the composition of those compounds instead,” says researcher Mats Olsson of Karolinska Institutet in Sweden. Regardless, the fact that the body gives off an odor when the immune system is activated is an important finding.

Olsson says that being able to detect these smells early on would allow us to potentially avoid dangerous illnesses. “There may be early, possibly generic, biomarkers for illness in the form of volatile substances coming from the body,” says Olsson. The ability to detect those who are sick through smell could also serve to protect healthy people from getting ill.


  1. Detecting sickness by smell. Psychological Science website. January 23, 2014. http://www.psychologicalscience.org/index.php/news/releases/detecting-sickness-by-smell.html.
  2. Olsson MJ, Lundstrom JM, Kimball BA, et al. The scent of disease: Human body odor contains an early chemosensory cue of sickness. Psychological Science. 2014; 0956797613515681. http://pss.sagepub.com/content/early/2014/01/21/0956797613515681.
  3. Rettner R. Body’s response to disease has a smell, study suggests. Live Science website. January 24, 2014. http://www.livescience.com/42836-smell-sickness-immune-system.html.