Steering clear of sick people is a good way to avoid getting sick. Now wouldn’t it be great if we could sniff out someone’s flu so we could avoid contracting it?

In this study, researchers investigated if people smelled differently when they were ill than when they were healthy. Participants collected body odours over two sessions – in one they were injected with saline and in the other with lipopolysaccharide (LPS), a toxin that actives the innate immune system. Their temperature and biomarkers for inflammation increased within hours of being injected with LPS. On the other hand, 40 other participants smelled eight body odour samples collected after LPS injection, eight collected after saline injection and two clean t-shirts that served as control, and rated them according to perceived intensity, pleasantness and healthiness. Control t-shirts were rated less intense, healthier and more pleasant than other samples. Participants’ body odours turned out to be more intense, more unpleasant and unhealthy after LPS injection. Stronger immune activation was associated with a higher rating of unpleasantness.

Findings suggest that sick people do give off chemical cues that indicate sickness which healthy people can detect and therefore allow them to avoid sick people.