Some People Claim to ‘Smell Cancer’ Before Diagnosis — Here’s the Science

Can people actually smell cancer before it’s diagnosed? It sounds like the kind of claim that belongs in a medical mystery, but scientists have spent years studying whether certain cancers produce distinct odors. Tumors can release chemicals known as volatile organic compounds (VOCs), and research has shown that dogs, and increasingly, specialized sensors, can sometimes detect them. Whether humans can do the same is far less clear.

That question resurfaced after a woman named Kate claimed she smelled her own cancer not once, but twice in her viral TikTok Video. Before being diagnosed with non-Hodgkin’s lymphoma and later thyroid cancer, she noticed a strange odor lingering on her clothes and bedsheets—one she described as a mix of rotting wood, cinnamon, and the aftermath of a hangover. According to her account, the smell disappeared after treatment and returned when cancer developed again. Her experience has reignited interest in a fascinating question: can cancer sometimes be detected by smell, and what does the science actually say?

@itstookate Yes, let’s put y’all’s apathetic jokes over a persons vulnerable experience that y’all are lucky to have shared with you. I’ve answered what it smells like in multiple follow up videos that can easily be found by clicking on the playlist at the bottom of this video named Cancer Smells. If it doesn’t show on your screen, it’s very easy to find at the top of my profile…come on guys.. let’s take the time to try to find things instead of not using your brain. Like, I’m BEGGING for y’all to fix your short-circuited dopamine addicted brains. #cancer #storytime #mentalhealth #healing #fyp ♬ original sound – itstookate🧿

Why Cancer Has a Smell: The VOC Explanation

Cancer cells exhibit altered metabolism, often growing and dividing faster than healthy cells, which changes the chemical waste products they generate. That acceleration produces a different chemical fingerprint compared to normal tissue. The mechanism behind cancer smell diagnosis involves a class of molecules called volatile organic compounds, or VOCs – small, carbon-based molecules that evaporate easily and exit the body through breath, urine, and skin. They’re produced through a process called lipid peroxidation, where reactive oxygen species (unstable molecules that damage cells) attack fats inside cancer cells and generate chemical byproducts as a result.

Gastroenterologists who specialize in colorectal cancer have noted for years that many patients with no oral conditions still develop a distinctive halitosis – bad breath – that carries a complex scent somewhat similar to rotten meat, though difficult to describe precisely. Researchers at Fudan University’s Minhang Hospital, writing in a 2025 letter in a gastroenterology journal, found significantly elevated dimethyl sulfide in the breath of colorectal cancer patients – a compound not typically elevated in people without the disease.

Specific compounds have also been identified across cancer types more broadly. Aldehydes like hexanal and heptanal are produced at different concentrations in cancer versus healthy cells. In lung cancer specifically, research has found that patients show elevated levels of acetone, isoprene, ethanol, hexanal, and dimethyl sulfide compared to healthy controls – a profile that a trained sensor or biological detector can, in theory, pick out from a breath sample.

What People Actually Report Smelling

Patient accounts of cancer smell diagnosis are anecdotal, not clinical evidence, but they follow consistent patterns across unrelated individuals. One woman who was later diagnosed with bilateral breast cancer described smelling what she could only compare to body odor in her armpit for months before her diagnosis. She showered daily but couldn’t get rid of the smell. After surgery, it stopped.

Another patient described a strong ammonia-type smell she could detect on herself – though no family member could smell anything when asked. She changed her diet and drank more water. Nothing stopped it. After her first lumpectomy, most of the smell was gone.

Reports vary significantly by cancer type. Some people describe fruity or sweet smells; others use words like “musty,” “metallic,” or “rotten.” An oncology professional described being able to detect gastrointestinal cancer on patients’ breath before they had received a diagnosis – attributing the smell to partially digested blood – and said the correlation had been correct every time it occurred.

No peer-reviewed evidence supports the idea that an untrained person can reliably detect cancer by smell on others, even though the underlying biology – cancer-altered VOCs – is real. These patient accounts are personal observations, not controlled findings. When people report detecting a smell on themselves, it may be because the VOC concentration is higher near the affected area, or because some individuals simply have more sensitive olfactory systems than average.

The Dog Detection Studies

Dogs are 10,000 to 100,000 times better at differentiating smells than humans, thanks to a far greater number of olfactory receptors and a more complex nasal anatomy. That sensitivity allows them to detect VOCs at concentrations measured in parts per trillion – far below what any current clinical instrument can reliably catch. The most compelling objective evidence that tumors produce a distinct odor signature comes from dog detection studies, which span two decades and cover multiple cancer types.

The earliest major study, a 2004 proof-of-principle trial published in the British Medical Journal, trained six dogs of mixed breeds over seven months to distinguish bladder cancer urine samples from healthy controls. The dogs correctly identified cancer samples on 22 out of 54 occasions – a 41% detection rate, compared to the 14% rate that pure chance would predict. The sample size was small (9 cancer samples per formal test run, drawn from 36 total cancer patients), and the researchers were explicit that this was a first step, not a diagnostic tool.

A decade later, accuracy had improved dramatically in a more rigorous cross-sectional study. Two three-year-old female German Shepherds, previously trained in explosives detection, were tested on 362 prostate cancer patients and 540 healthy controls at an Italian teaching hospital and military veterinary center. According to a 2015 study published in the Journal of Urology, one dog reached 100% sensitivity and 98.7% specificity; the second achieved 98.6% sensitivity and 97.6% specificity. This was a cross-sectional diagnostic accuracy study – not a prospective clinical trial – which means the results reflect performance under controlled laboratory conditions rather than real-world screening.

More recently, a single dog trained over one year was tested in a double-blind clinical trial on 246 participants, including 41 lung cancer patients across all disease stages and 205 healthy controls. Combining breath and urine samples, the dog correctly identified 40 of the 41 cancer cases, reaching a 97.6% overall detection rate, according to a 2021 study published in BMC Cancer. And in a 2025 study from India involving 1,502 participants, canine detection combined with a statistical method called Bayesian modeling – which refines probability estimates based on multiple pieces of evidence – achieved high accuracy for identifying multiple cancer types from breath samples alone.

Across these studies, a consistent picture emerges: cancer produces a VOC signature measurable in urine and breath, and trained animals can reliably distinguish it from healthy samples under controlled conditions. Whether that reliability holds up in real-world clinical screening, across populations and labs, remains an open question. Researchers have also noted in animal models that tumor-related odor signals appear in urine at around week 5 of tumor development and in breath-based odor at around week 13 – pointing to a detection window well before tumors reach a size that conventional imaging would flag.

Building a Machine That Can Do What Dogs Do

Training a detection dog takes a year or more. Individual animals vary. You can’t run 10,000 breath samples through a Labrador in an afternoon. So researchers have been building electronic versions of the canine nose, known as eNoses (electronic noses).

Electronic noses create “smell fingerprints” – recognizable chemical profiles – and have demonstrated high accuracy detecting lung, head and neck, and colorectal cancers from breath samples. They work by using arrays of chemical sensors that each respond to different molecules. The combined signal from multiple sensors produces a profile that machine learning algorithms can compare against known cancer and non-cancer samples.

A 2025 multicentre study in Annals of Oncology prospectively validated an eNose model for lung cancer detection across multiple hospitals, confirming that eNose analysis of exhaled breath enables accurate lung cancer detection at thoracic oncology outpatient clinics, regardless of tumor characteristics, disease stage, or which diagnostic center conducted the test. One clinical trial on the Aeonose device, a commercially developed eNose system, demonstrated 84% sensitivity and 97% specificity in detecting lung cancer via exhaled VOCs.

Exhaled breath is a significant focus of this research because it provides a non-invasive sample that reflects VOC exchange in the lungs, making it especially promising for detecting lung and esophageal cancers. Patients simply breathe into a collection device – no needle, no scope, no radiation.

Read More: 20 Early Warning Signs of Cancer

Where the Science Currently Stands

No VOC-based tests are currently in clinical use for early cancer smell diagnosis, despite the strength of some individual studies. The barriers are largely technical and regulatory. Challenges for FDA approval include a lack of standardized breath collection protocols, inconsistent analytical standards, and problems with reproducibility across different labs and patient populations. A test that works brilliantly at one hospital may perform differently at another if the breath samples aren’t collected and analyzed the same way.

The FDA has approved certain VOC breath biomarkers – including ethanol, hydrogen, nitric oxide, carbon monoxide, and some branched hydrocarbons – for specific diagnostic purposes, but none of these approvals extend to cancer detection specifically. The regulatory pathway for a cancer-specific breath test remains open but uncleared.

Breath-based VOC analysis does offer genuine advantages: speed, patient safety, low cost, and the ability to repeat testing without the burden of invasive procedures. The question is not whether the science is real – it clearly is – but whether researchers can solve the standardization problem well enough to satisfy regulators.

Paying Attention to What Your Body Is Telling You

If you’ve noticed an unexplained change in your own body odor – something persistent that showers don’t resolve and that doesn’t track with any obvious lifestyle change – that’s worth mentioning to a doctor. It won’t be the basis of a diagnosis on its own, and no doctor will confirm or rule out cancer by smell alone. But the accounts from patients who experienced exactly this, often months before imaging or biopsy caught anything, are consistent enough that the observation deserves to be part of the clinical conversation rather than dismissed.

Cancer leaves chemical traces in the body well before it becomes visible or symptomatic in conventional ways. The VOC changes that produce a detectable odor signature begin early in tumor development – measurably so in animal models before any scan would flag a mass. That’s the entire biological premise behind breath-based diagnostics. You don’t need a trained dog or a clinical eNose to act on it. If something about your body has changed in a way you can’t explain – persistent smell, unusual breath, unexplained odor from a specific area – document it, date it, and bring it to your next appointment.

Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.

AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.

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