This study divided volunteers into two groups; one group received sham treatment with saline injection, the second group injected with lipopolysaccharide. Both groups wore T-shirts for 4 hours. A second group asked to evaluate the smell of the shirts rated the LPS t-shirts as having an unpleasant and unhealthy smell.
The Scent of Disease
Human Body Odor Contains an Early Chemosensory Cue of Sickness
Observational studies have suggested that with time, some diseases result in a characteristic odor emanating from different sources on the body of a sick individual. Evolutionarily, however, it would be more advantageous if the innate immune response were detectable by healthy individuals as a first line of defense against infection by various pathogens, to optimize avoidance of contagion. We activated the innate immune system in healthy individuals by injecting them with endotoxin (lipopolysaccharide). Within just a few hours, endotoxin-exposed individuals had a more aversive body odor relative to when they were exposed to a placebo. Moreover, this effect was statistically mediated by the individuals’ level of immune activation. This chemosensory detection of the early innate immune response in humans represents the first experimental evidence that disease smells and supports the notion of a “behavioral immune response” that protects healthy individuals from sick ones by altering patterns of interpersonal contact.