A change in odor – Subtle differences occur in body odor when someone is sick, or infected, changing their odors from pleasant to aversive. When picked up by others, these differences can inform them to protect themselves and avoid becoming infected themselves.
Active immune systems – The change in odor is thought to be caused by activation of the body's innate immune system, in response to a new infection. Scientists at the Karolinska institute in Sweden injected volunteers with a compound mimicking the presence of bacteria and changes in smell were detected.
Sniffing out disease – Everyone has their own "odorprint" made up of select compounds combining together to release a unique odor. But this scent based on various factors including age, gender and health.
Smell for protection – Smelling sickness can help people avoid infection from others, but new research has also revealed that sniffing an infection in others could also initiate an immune reaction and prepare the body for attack.
Signature scents of disease – Several diseases have been discovered to have signature scents, including people with typhoid fever reported to smell like baked bread, people with yellow fever smelling like a butcher's shop and the glandular disease Scrofula leaving people smelling like stale beer. Pictured, a patient with typhoid fever.
Not just body odor – Odors are release not just from skin but also the breath, blood and urine. Recent studies at the Karolinska Institute further revealed that the smell of urine is also affected by inflammation processes within the body. Urine could therefore also distinguish between the healthy and unhealthy.
Bated breath – The team's next target is human breath, known to change when someone is sick, but this is harder to sample and for people to rate.
Seeking out cancer – Cancer cells are thought to release compounds that differ to healthy cells, enabling a change in smell to be picked up -- potentially at early stages of development. At this level of subtlety, however, the human nose is ruled out. The greater sense of smell in dogs is being harnessed instead.