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can you smell sickness? study shows human scent can actually detect infection

it’s commonly known that animals can sniff out diseases, but is the human nose just as capable?

by angelica bottaro

published mar 22, 2024

5 minute read

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5 minute read

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dogs have also been known to have a knack for sniffing out sickness. getty images

sickness has a scent, and new research shows that canines aren’t the only mammals with enough olfactory prowess to sniff out illness and disease in people. a study published in evolution, medicine, & public health looked at the power of human scent and its ability to pick up on acute respiratory infections, with results showing that, while not as significant as other animals on the planet, the human nose is well able to detect the scent of sickness in others.

so, what does this mean? well, the published findings may be able to further research surrounding humans and their capabilities to ward off infections while paving a path to better reduction techniques when it comes to the spread of endemic and pandemic-like infections.

diseases and their unique odours

it’s not exactly news that diseases have their own unique aromas. for example, studies published nearly three decades ago have already outlined different smells correlated with specific illnesses and health conditions.

for example, diabetic ketoacidosis, a potentially life-threatening complication of diabetes, offers up a smell that mimics that of rotting apples. yellow fever may smell more like meat hanging in a butcher shop, whereas typhoid fever hits the nose like freshly baked bread. other diseases and their correlating smells include:

scrofula: stale beer
rubella: plucked feathers
diphtheria: sweetness
pellagra: sour bread
favus: mousy
candida: heavy sweetness
advanced liver disease: musty

prior to the medical advancements of today, healthcare providers of yesteryear relied heavily on the nose’s unique abilities as part of the diagnostic process for infectious diseases or other chronic health conditions. in fact, smell has been used to detect disease as far back as the time of hippocrates, a greek physician born in 375 b.c.

the long-gone sniffing out of infectious diseases may have made its way out of medical schools over the many years since its inception, and considering many of the infections mentioned above are no longer prevalent in today’s society, it’s not surprising that the good work of the nose was put to bed.

that said, the role of olfactory senses in helping to make diagnoses, especially regarding respiratory infections, may be more significant than once thought, even with the medical advancements of today.

the connection between a sense of smell and respiratory infections

the immune system is a robust collection of fighter cells, each tasked with its own job to keep the body safe from infection and disease. when coming into contact with a pathogen, the immune system begins the process of alerting the body to the threat, attacking it where it lies, and expelling it from the system before it can do any severe damage.

when the system activates, it causes those pesky symptoms people have to contend with while overcoming the illness, such as fever, fatigue, and loss of appetite. this metabolically costly process drives signs and behaviours of sickness. alongside the main actions of the immune system are other defences that have since gone unutilized in the wake of new technologies, one being a nose for infections.

the study examining the connection between smell and respiratory infections theorizes that the immune system uses olfactory responses to illness in two ways: to help the immune system prepare for battle and to facilitate behaviours that limit the spread of infection, such as warning people that someone is sick and that they should maybe stay away from them.

it is the same basic principle of sight and sickness. people who are ill often develop physical characteristics such as paleness and drooping eyelids. these signs, visible to the naked eye, drive behaviours such as avoidance in an effort to limit the spread of contagious diseases.

when it comes to sense of smell, it all comes down to body odour. body odour is made up of molecular compounds, called volatile organic compounds or vocs, that are released in various ways: saliva, urine, feces, the skin, and blood.

when a person is ill, vocs change in such a way that the scent that comes out with them changes, too. the newest data has found that these vocs are directly altered by diseases, leading to different smells when a person develops a new illness. one specific example cited in the study found that people with mycobacterium tuberculosis changed the voc output in the breath, leading to an odour distinguishable from healthy people.

other factors, such as temperature, also play a role in the nose’s ability to detect illness in others. people with higher body temperatures, such as those who develop fevers, are more likely to emit a sicker-smelling body odour, giving people even more of a chance to identify sickness in others using only their sense of smell.

since worse symptoms are often associated with more severe infections, the research indicates that the sicker a person is, the more likely they are to indirectly drive behavioural changes in others trying to avoid pathogenic infections.

smelling 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 to share with friends at happy hour. if developed enough, the skill could be used to avoid the spread of infectious diseases in humans in the same way that animals use their sense of smell.

when looking at other mammals, particularly rodents, research has found that they have quite the nose for sick individuals. this gives them the unique ability to avoid those who may pass on pathogens simply by taking a whiff. so, to put it simply, the smell of sickness enables rodents to change their behaviours to avoid illness and thus improve their rates of survival.

within humans, the body is primed and ready to fight if the aroma of sickness reaches the nostrils, but it is still up for investigation if people can use their sense of smell to overtly change their behaviours in a way that avoids sickness altogether.

with the current level of research, it’s difficult to determine just how useful it is to identify sickness in others through scent alone, but there’s no denying the science. the human nose can smell when another person’s immune system is working hard to rid the body of a pathogen, and when that aroma reaches the senses, it signals to its own immune system that something wicked this way comes, and it’s time to prepare for war.

angelica bottaro

angelica bottaro is the lead editor at healthing.ca, and has been content writing for over a decade, specializing in all things health. her goal as a health journalist is to bring awareness and information to people that they can use as an additional tool toward their own optimal health.

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can you smell sickness? study shows human scent can actually detect infection

it’s commonly known that animals can sniff out diseases, but is the human nose just as capable?

diseases and their unique odours

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