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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.

Teenager's nose close up.Asier Romero/Shutterstock

Does disease smell?

Body odor can be a sign of more than just forgetting to put on deodorant. Researchers have long known that certain illnesses including cancer, multiple sclerosis, and Parkinson’s disease, cast particular odors, 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. Make sure you know about these diseases that doctors miss the most.

Closeup of nose and cheek.Geinz Angelina/Shutterstock

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.”

Doctor coat with stethoscope.sheff/Shutterstock

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. 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. And while that research is promising, don’t believe these health myths that make doctors cringe. Now, check out the diseases we can already detect through smell.

Doctor measuring blood pressure of a patient.LeventeGyori/Shutterstock

Preeclampsia

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 2016 study in 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.

Clinician listening to patient's lungs with a stethoscope.Dmytro Zinkevych/Shutterstock

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 “odor” 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 2016 in the journal ACS Nano. And, for when you don’t want to lead with an odor, here’s a dentist’s tips for beating bad breath.

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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, an assistant professor of chemical and biomolecular engineering at the University of Illinois. Watch out for these other silent signs your body might be in big trouble.

Beads of sweat on someone's back.Anna Lo/Shutterstock

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 the odor will be like raw fish.

Physiotherapist examining a spine model in the clinic.wavebreakmedia/Shutterstock

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 2017 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 found that it predicted the disease by up to 90 percent.  Now learn the other silent symptoms of MS.

A woman in bed with the flu.Rawpixel.com/Shutterstock

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, published in 2017, participants could identify sick versus healthy people simply by smelling their body odor and looking at photographs of their faces for visual cues, such as skin pallor.

African male patient getting dental treatment in dental clinic.V_Lisovoy/Shutterstock

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.” These are the shocking diseases that eye doctors find first.

Person with diabetes using a test strip to check his blood sugar level by glucometer at home.Syda Productions/Shutterstock

Diabetes

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.

Teenage boy covering the mouth with his hand.JJFarq/Shutterstock

Mono

The Epstein-Barr virus strikes about 90 percent of the population worldwide. Some of the time, it leads to infectious mononucleosis, or mono. For some people with mono, sour breath is among the first signs, Dr. Hirsch says. Check out 11 more silent warning signs of mono.

Two salmon steaks with thyme in a pan with ice.Kovenkin/Shutterstock

Trimethylaminuria

Also known as fish-odor 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 odor can lead to social isolation, depression, and emotional disorders.

Middle-aged psychologist sitting next to a patient.Pressmaster/Shutterstock

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. And while those facts are true, don’t believe these myths about mental health.

Cute baby lying on tummy in parents' bed.Monkey Business Images/Shutterstock

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. Doctors are also trained to be observant, and this is what they can tell by just looking at you.

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Medically reviewed by Michael Spertus, MD, on September 19, 2019