When a person is sick, VOCs change in such a way that the scent released changes accordingly. The latest data suggests that these VOCs are directly altered by disease, causing people to smell differently when they develop a new disease. One specific example cited in the study found that people with tuberculosis bacteria change their VOC output in their breath, causing them to smell distinctly from healthy people.
Other factors, such as temperature, also affect the nose's ability to detect illness in others. People with high body temperatures, such as those with a fever, are likely to have a fouler body odor, which makes it much more likely that they can identify illnesses in others using only their sense of smell.
Because worse symptoms are often associated with more serious infections, studies have shown that the sicker a person is, the more likely they are to indirectly induce behavioral changes in others to avoid pathogenic infections.
Smell sickness: future directions.
Being able to smell a sick person is interesting in and of itself, but it's more than just a fun anecdote you can share with friends during happy hours. If sufficiently developed, this technology could be used to prevent infectious diseases from spreading to humans in the same way that animals use their sense of smell.
When looking at other mammals, especially rodents, studies have shown that their noses are very good for sick people. This gives them the unique ability to avoid people who can transmit pathogens simply by smelling them. Simply put, disease odor allows rodents to change their behavior to avoid disease and increase survival rates.