Some cancers do produce a detectable odor, but it is not reliable enough for diagnosis
Yes, certain cancers can create a smell that other people may notice. The odor typically comes from dead or dying cancer cells, infected tissue around the tumor, or changes in how the body breaks down chemicals. However, the smell is usually faint, varies widely between people, and depends on the cancer type and stage. A smell alone cannot tell you whether someone has cancer — and most people with cancer produce no noticeable odor at all.
The idea that cancer has a smell is not new. Doctors in the 1600s and 1700s wrote about patients with certain tumors having a distinctive odor. Modern research has confirmed that some cancers do release volatile organic compounds — chemicals that evaporate into the air — but detecting them requires sensitive equipment, not a human nose.
Key Takeaways
- Certain cancers, particularly those affecting the skin, breast, or colon, may produce a faint odor that some people can detect, but the smell is not consistent or strong enough to diagnose cancer.
- The odor comes from dead cancer cells, bacterial growth in infected tissue, or metabolic changes in the body, not from the cancer itself.
- Dogs have been trained to detect cancer-related odors in breath or urine samples with accuracy rates between 65 and 97 percent, depending on the cancer type.
- If you notice an unusual or persistent body odor in yourself or someone else, the cause is usually a treatable infection or skin condition, not cancer.
- A change in smell should never replace standard screening or medical evaluation — it is not a substitute for blood tests, imaging, or physical exams.
Which cancers are most likely to produce an odor
Cancers that affect the skin surface or break down tissue are more likely to create a noticeable smell. Melanoma and other skin cancers can produce an odor when the tumor ulcerates, or breaks open, and bacteria colonize the wound. Breast cancer can sometimes create a smell if the tumor erodes through the skin. Colorectal cancer and other gastrointestinal cancers may produce odors in breath or stool because of how the tumor affects digestion and bacterial growth in the gut.
Cancers that remain internal and do not break through tissue — such as early-stage lung cancer or pancreatic cancer — typically produce no detectable odor. The stage of the cancer matters too: advanced cancers that have grown large or begun to ulcerate are far more likely to produce a smell than small, contained tumors.
What causes the smell
The odor does not come from the cancer cells themselves, but from what happens around them. When cancer cells die, they release compounds into the bloodstream and tissues. The body's immune response to the tumor can also trigger inflammation and bacterial growth. If the tumor breaks through the skin or tissue, bacteria can infect the wound, which produces its own strong odor.
In some cases, the cancer changes how the body metabolizes food or processes waste. Colorectal cancers, for example, can alter the bacteria in the colon and the breakdown of digestive material, leading to changes in stool odor or breath. Lung cancers may affect how the lungs clear mucus, creating a change in breath odor. These metabolic shifts produce volatile organic compounds — the same chemicals that give rotting food or infected wounds their distinctive smells.
Can dogs detect cancer by smell
Dogs have a sense of smell roughly 10,000 to 100,000 times more sensitive than humans. Researchers have trained dogs to detect cancer-related odors in breath samples, urine, or skin swabs. Studies have reported detection rates between 65 and 97 percent, depending on the cancer type and how the study was designed.
The most reliable results have come from studies of bladder cancer and ovarian cancer, where dogs detected the odor in urine or breath samples with high accuracy. Dogs have also shown promise in detecting breast cancer and lung cancer. However, these studies have been small, and the results have not been consistent enough to use dogs as a screening tool in clinical practice. A dog's alert is not a diagnosis — it would need to be followed by standard medical testing.
Why smell is not a reliable way to detect cancer
The smell produced by cancer is too faint and too variable for humans to use as a detection method. Two people with the same cancer type may produce different odors, or no odor at all. The smell can also be confused with other conditions: an infected wound, poor hygiene, a urinary tract infection, or bacterial overgrowth can all produce similar odors. A doctor cannot tell the difference between these causes by smell alone.
Additionally, most cancers do not produce any detectable odor, even at advanced stages. Relying on smell to detect cancer would miss the vast majority of cases. This is why screening tests — mammograms for breast cancer, colonoscopies for colorectal cancer, blood tests for various cancers — are far more effective. These tests are designed to find cancer before it grows large enough to produce symptoms or odors.
What to do if you notice an unusual odor
An unusual or persistent body odor is far more likely to be caused by a treatable infection, poor hygiene, a skin condition, or a metabolic disorder than by cancer. Common causes include bacterial or fungal infections, urinary tract infections, poor wound healing, and hormonal changes. Some medications and dietary choices can also affect body odor.
If you notice a new or unusual odor in yourself or someone else, the first step is to see a doctor. They can examine the area, ask about other symptoms, and order tests if needed. Do not assume the odor means cancer is present. A doctor will consider the full picture — how long the odor has been present, whether there are other symptoms, the person's age and medical history, and the results of a physical exam — before recommending any further testing.
How cancer is actually diagnosed
Cancer diagnosis relies on specific, evidence-based tests, not on symptoms like odor. The process usually begins with a physical exam and a description of symptoms. From there, a doctor may order imaging tests such as X-rays, CT scans, or ultrasounds to look for tumors. Blood tests can detect certain cancer markers — proteins or other substances that cancer cells release into the bloodstream.
The only way to confirm a cancer diagnosis is with a biopsy, a procedure in which a small sample of tissue is removed and examined under a microscope. A pathologist looks at the cells to determine whether they are cancerous and, if so, what type of cancer it is. This tissue diagnosis is the gold standard and cannot be replaced by smell, imaging, or blood tests alone.
Frequently Asked Questions
Can I smell cancer on someone else's breath?
Possibly, but only if the cancer is advanced and affecting the lungs, mouth, or digestive system. Even then, the odor is usually very faint and easily confused with bad breath from other causes, such as gum disease or dry mouth. A change in someone's breath odor should prompt a doctor's visit, but it is not a sign of cancer unless other symptoms are present.
Does all cancer smell bad?
No. Most cancers produce no detectable odor at all, even at advanced stages. Only cancers that break through tissue, affect the digestive system, or create infected wounds are likely to produce a smell. Early-stage cancers almost never do.
If I have an unusual smell, does that mean I have cancer?
No. Unusual body odor has many causes, most of them treatable and not cancer-related. Infections, poor hygiene, hormonal changes, and certain medications are far more common causes. See a doctor to find out what is causing the odor, but do not assume it is cancer.
Should I get screened for cancer if I notice a smell?
If you notice a new or unusual odor, see your doctor first. They can examine you and determine whether screening is needed based on your age, medical history, and other symptoms. Standard screening tests — not smell — are what actually detect cancer early.
Are there electronic devices that can smell cancer like dogs can?
Researchers are developing electronic "noses" that can detect volatile organic compounds associated with cancer, but these devices are still in the research phase. They are not yet available for routine screening or diagnosis. When and if they become available, they would be used alongside standard tests, not instead of them.