12 Diseases Doctors Can Actually Detect Through Smell

Many diseases and conditions have their own “breathprint,” and this may soon pave the way for earlier detection and diagnosis.

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diseases doctors can smell
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Does disease smell?

Body odor can be a sign of more than just someone forgot to put on their deodorant. Researchers have long known that certain illnesses including cancer, multiple sclerosis, and Parkinson’s disease, cast particular odours, says Alan Hirsch, MD, the Neurological Director of the Smell & Taste Research and Treatment Foundation in Chicago. While scent tests to diagnose disease are not quite ready for prime time, research is ongoing, says Dr. Hirsch, also the author of several books including Nutrition and Sensation.

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pores on the face. oily skin of the face

Why do diseases smell?

Diseases change the way a body works, says Yehuda Zeiri, PhD, a biomedical engineer at Ben-Gurion University’s Kiryat Bergman Campus in Be’er-Sheva, Israel. “When disease leads to enhancement of new and different biochemical processes in the body, these processes may lead to the production of small volatile molecules,” he explains. “These [molecules] can be transported by the blood to the lungs and be released in exhaled breath; they can also be released in the urine and sweat.”

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Doctor coat with stethoscope

Diagnosing diseases through smell

Researchers are developing ways to detect the scent of disease. “According to the scientific literature there is evidence that the scent may contain markers for lung cancer, breast cancer, diabetes, melanoma, and more,” Dr. Zeiri says. (Dogs have actually been trained to detect cancer.) In the future, doctors may be able to spot cancer, diabetes, kidney disease, and a host of other conditions solely by their smell—and well before other symptoms show up. Here are some of the conditions that doctors can now—or will soon—detect by smell.

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Doctor measuring blood pressure of a patient


Pregnancy-related high blood pressure—preeclampsia—is an early warning sign of deadly eclampsia, which is why it’s so important to spot the condition early. A study in a 2016 issue of Advanced Materials Science showed that researchers could detect preeclampsia with 84 percent accuracy based on a mother’s “breathprint”—like your fingerprint, your breath contains unique markers that can reveal a lot about your health. (According to one study, eating dark chocolate can help prevent preeclampsia.)

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Learned focused therapist examining patients lungs

Lung cancer

There is compelling research that indicates lung cancer can be detected by smell, Dr. Hirsch says. An invention called “NaNose”—a breathalyzer-type device developed by an Israeli company—is up to 90 percent accurate at diagnosing lung cancer; the device detects a special “odour” emitted by the cancer cells. Doctors can use the same technology to identify Parkinson’s disease, other cancers, kidney failure, multiple sclerosis, and Crohn’s disease—and the accuracy rate is at 86 percent, according to a study published in the journal ACS Nano. This is what an oncologist wants women to know about lung cancer.

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Hands massaging female abdomen.Therapist applying pressure on belly. Woman receiving massage at spa salon

Kidney failure

Ammonia on the breath is a sign of kidney failure. University of Illinois researchers have developed a disposable device that can detect the breathprint of kidney failure and potentially get people to a doctor sooner—when treatment will be more effective. “In the clinical setting, physicians use bulky instruments, basically the size of a big table, to detect and analyze these compounds. We want to hand out a cheap sensor chip to patients so they can use it and throw it away,” says professor Ying Diao, PhD, a professor of chemical and biomolecular engineering at Illinois, in a news release. A kidney infection could start from something as simple as a UTI. These are silent signs you have a UTI.

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Beads of sweat are forming on the back. Disposition to sweating or perspiring.

Liver failure

When your liver stops doing its job and processing toxins, contaminants will build up in your urine, perspiration, and even your breath—and odour will be like raw fish.

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Physiotherapist examining a spine model in the clinic

Multiple sclerosis

MS is an autoimmune disease, where the body begins attacking its own central nervous system. The resulting nerve damage can cause numbness, tingling, and problems with vision and gait. The condition is most often diagnosed by magnetic resonance imaging (MRI) of the brain or a “spinal tap,” but MS may also have its own distinct breathprint, according to a report in ACS Chemical Neuroscience. In the study, exhaled breath was collected from 146 people with MS and 58 people without this progressive disease—and researchers identified a clear pattern. MS is actually one of the most common autoimmune diseases in Canada.

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A sick woman in bed

Infectious disease

Worried that you should put some space between you and your spouse or a co-worker who might be coming down with the flu? Give ’em a sniff, according to a small study in the Proceedings of the National Academy of Sciences. In this study, participants could identify sick versus healthy people simply by smelling their body odour and looking at photographs of their faces for visual cues, such as skin pallor.

If you’re wondering whether you have a cold or the flu, here’s how to tell.

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African male patient getting dental treatment in dental clinic

Gum disease

If you have an infection in your gums, the bacteria releases waste products such as hydrogen sulfide, which smells like rotten eggs, explains Dr. Hirsch. “This smell tells us that the person has gum disease, a dental abscess, or poor oral hygiene,” he says. “The abscess could be hidden in a crevice that is hard to find on an X-ray, but the scent can encourage your dentist to look harder and order a panoramic X-rays to find the culprit.” Better yet, catch gum disease early by knowing the signs.

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medicine, diabetes, glycemia, health care and people concept - close up of man checking blood sugar level by glucometer at home


People with diabetes can have a fruity smell to their breath, Dr. Hirsch says. This can signal diabetic ketosis: When there isn’t enough of the hormone insulin or the body isn’t using it correctly, we start burning fat for fuel. This can lead to potentially fatal ketoacidosis if not caught and addressed early.

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Boy covering the mouth with his hand


Infectious mononucleosis or mono strikes about 90 percent of the population worldwide; for some people, sour breath is among the first signs, Dr. Hirsch says.

Learn more about the silent signs of mono.

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Two salmon steaks with thyme in a pan with ice.Red fish.


Also known as fish-odour syndrome, trimethylaminuria is a rare metabolic disorder that occurs when a person can’t digest certain foods, including eggs, liver, legumes, fish, and some vegetables. As the foods sit undigested in the intestines, trimethylamine builds up and is expelled in bodily fluids like sweat and saliva, Dr. Hirsch explains. The smell is described as similar to rotting fish, urine, days-old garbage, or rotten eggs. It’s not a life-threatening condition, but the unpleasant odour can lead to social isolation, depression, and emotional disorders.

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Middle-aged psychologist sitting next to his patient and listening to her childhood story in order to find reason of her disease

Psychiatric illness

Bad breath often accompanies schizophrenia and other severe types of psychosis, Dr. Hirsch says. “These individuals are fearful of others and one of the ways they may keep people away is by not bathing,” he says. Not taking care of one’s self can also signal a relapse.

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Cute Baby Lying On Tummy In Parent's Bed

Maple syrup disorder

Babies born with this genetic disorder can’t break down certain parts of proteins and, as a result, their urine, ear wax, and other bodily fluids may smell like maple syrup, Dr. Hirsch says. Next, learn about 11 things doctors can tell just by looking at you.

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