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. Shutterstock
The change in odor is thought to be caused by activation of the body's 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. MICHAEL KAPPELER/AFP/Getty Images
Everyone has their own "odorprint" made up of select compounds combining to release a unique odor. But this scent is based on various factors including age, gender and health. DON EMMERT/AFP/AFP/Getty Images
Smelling sickness can help people avoid infection from others, but research has also revealed that sniffing an infection in others could initiate an immune reaction and prepare the body for attack. Robert Cianflone/Getty Images Europe/Getty Images
Several diseases have been discovered to have signature scents: People with typhoid fever are said to smell like baked bread, people with yellow fever smell like a butcher's shop, and those with the glandular disease scrofula smell like stale beer. Pictured, a patient with typhoid fever. JAY DIRECTO/AFP/Getty Images
Odors are release not just from skin but also breath, blood and urine. Recent studies at the Karolinska Institute further revealed that the smell of urine is affected by inflammation processes within the body. Urine could therefore distinguish between the healthy and unhealthy.
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. STAN HONDA/AFP/Getty Images
Cancer cells are thought to release compounds that differ from healthy cells, enabling the detection of a change in smell, potentially at early stages of development. At this level of subtlety, however, the human nose is ruled out. Dogs' greater sense of smell is being harnessed instead. John Bonifield/CNN