You Can Actually Smell Sickness

So it's not exactly X-ray vision or mind reading, but average humans apparently have a pretty advanced ability: smelling sickness. New research suggests that people are able to detect sickness via smell in someone whose immune system is highly active. Take a big whiff, folks — certain diseases have particular scents. Those with diabetes reportedly have breath that smells like acetone or rotten apples. Scrofula, a tuberculosis infection, is often associated with stale beer, and yellow fever smells like a butcher's shop. Lovely.

Researchers at the Karolinska Institutet in Sweden say this olfactory wonder may help humans to avoid illness. The team injected eight people with either a toxin or a saline solution. Lipopolysaccharide, the toxin made from bacteria, is known for ramping up the immune system. Each participant wore tight shirts, waiting for Mother Nature to do her magic. Those with the toxin noticed higher body temperatures and increased levels of cytokines, a group of immune system molecules.

But the real test was with the lucky volunteers, a group of 40 participants, who got to smell the sweat samples. The verdict? They found those injected with the toxin had a more intense and unpleasant smell, and they also gave off an odor that was "unhealthier" than the people injected with just saline.

Researchers say this is "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."

The greater a person's immune system response, the funkier they get. Volunteers were able to note the change just a few hours after the body's reaction was triggered. When scientists examined the number of odorous compounds in the both sample sets, they found no differences, which could mean the differences in odor isn't due to the amount, but the compounds' composition.

While the precise elements are yet to be identified, they say people definitely give off an "aversive signal." So, if the stranger next to you on the bus just switched seats, you might want to consider a trip to the doctor for a check-up.