Although there have been some reports of people with certain diseases giving off a smell after symptoms appear (such as Yellow fever, which one study said smells like a "butcher's shop"), the new findings suggest that "humans can indeed dissociate between the odors of sick and healthy individuals," within four hours after the immune system is activated, the researchers, from the Karolinska Institutet, wrote in the Jan. 22 issue of the journal Psychological Science.
The scientists also found that the greater the participant's immune response to the toxin, the greater the unpleasant rating the sample received.
"Taken together, these results strongly support that humans emit a chemical cue during a generalized sickness response that can be perceived by others," the researchers said.
The ability to detect sick people by their smell could serve a purpose by protecting healthy people; it would help them avoid sick individuals, the researchers said.
However, because the new study was conducted in a lab, and participants were injected with a single toxin, it's not clear whether the same results would be seen outside the lab in people who have other infections.