How your smell can reveal if you're sick

By Meera Senthilingam, for CNN

Updated 2034 GMT (0434 HKT) January 20, 2016

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.
Photos: How humans smell disease to stay healthy
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.
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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.
Photos: How humans smell disease to stay healthy
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.
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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.
Photos: How humans smell disease to stay healthy
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.
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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.
Photos: How humans smell disease to stay healthy
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.
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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.
Photos: How humans smell disease to stay healthy
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.
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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.
Photos: How humans smell disease to stay healthy
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.
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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.
Photos: How humans smell disease to stay healthy
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.
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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.
Photos: How humans smell disease to stay healthy
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.
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Story highlights

  • Smell can reveal when someone is sick due to changes in their immune activity
  • Body odor will vary depending on age, diet, sex, metabolism and health
  • A person's smell escapes not just from their skin but their breath, blood and urine