Being around sick people may make us smell.
When healthy mice are exposed to ill rodents, their odour changes to match the scent of the sick animals, a study found.
This is thought to be an evolutionary advantage among animals that live in groups that warns others a disease may be spreading.
The scientists believe their findings could help to detect and diagnose diseases in both humans and animals.
Being around sick people may make us smell to warn others of the risk of disease (stock)
‘Exposure to the odors of sick individuals may trigger protective or preparative responses in their social partners to minimise the risk of impending infection,’ said lead author Dr Stephanie Gervasi, from the Monell Center, Philadelphia.
Mice were injected with a molecule from E.coli bacteria. They were then put in cages with healthy rodents.
Within a few hours, the injected animals showed signs of sickness, including fatigue and weight loss, but were not contagious.
When a third group of specially trained ‘sniffer’ mice was introduced, they correctly identified the urine of the sick animals versus that of the healthy rodents 90 percent of the time.
The sniffer mice also identified the urine of rodents who had been exposed to sick animals but were otherwise healthy in 63 percent of cases.
When the compounds in the different urine samples were analysed, 75 percent of those from the exposed but healthy mice were chemically similar to urine from the ill rodents.
This suggests that both the scent and chemical make-up of urine changes when a healthy animal is around a sick one.
The results were published in the journal Scientific Reports.
‘This work shows not only that odours signal disease but that they can have strong effects on individuals that detect them,’ study author Dr Gary Beauchamp said.
‘This is a remarkable transfer of information via olfaction that specifically alters physiology and could play a role in disease transfer among individuals in many species.’
The findings build on previous research that suggests the odour given off by rodents with cancer reduces the immunity of surrounding healthy animals.
Male mice infected with certain parasites also give off a scent that makes their female counterparts more tolerable of pain.
This comes after scientists discovered last July why certain smells cause people to vividly recall memories.
Information about time and space is stored in the same region of the brain where odours are processed, which may help people remember their ex’s perfume when they reminisce about a particular date, a study by the University of Toronto found.