The Scent of Disease

TLDR

Observational studies indicate that diseases can produce characteristic body odors over time, and evolutionarily, an innate immune response detectable by healthy individuals would aid in avoiding contagion. The authors activated the innate immune system in healthy volunteers by injecting endotoxin (lipopolysaccharide). Within hours, endotoxin exposure produced a more aversive body odor, an effect mediated by immune activation, providing the first experimental evidence that disease smells trigger a behavioral immune response that alters interpersonal contact.

Abstract

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.