Millions of Americans skip cancer screening because it feels invasive, awkward or easy to postpone. Only about 65 percent of eligible adults are currently up to date on colorectal cancer checks.
Stool-based kits sit unopened in bathroom drawers, and the 45th-birthday reminder rarely turns into a colonoscopy appointment on its own.
A new study from South Korea aims at exactly that reluctance. Researchers analyzed saliva and stool samples from 507 people and found a simple mouth rinse could flag both colorectal and stomach cancer more sensitively than the standard fecal test.
The findings appeared online on August 20, 2026, in the journal Cell Host and Microbe. The team built a diagnostic tool they call the mouth-to-feces index.
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It measures how many identical bacterial variants show up in a person's saliva and in their stool.
When mouth bacteria leak into the gut
Under normal conditions, saliva, stomach acid and resident gut bacteria keep oral microbes from setting up shop lower down. Inflammation and immune changes can weaken those barriers.
In the study, the index ran 2.6 to 3.0 times higher in patients with gastric or colorectal cancer than in healthy volunteers.
It did not rise in the 215 participants with metabolic disorders such as type 2 diabetes, hypertension or high cholesterol. That specificity matters. It means the signal appears to track cancer rather than general inflammation.
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Higher sensitivity than the stool test
When researchers tested how well oral samples alone could identify colorectal cancer, sensitivity reached 92.9 percent. The fecal occult blood test, one of the most common at-home screens, hit 61.0 percent in the same comparison.
Stool-based screens can miss cancers when tumors are not bleeding at the moment of the test, and they can flag false positives from other causes.
The full cohort of 507 included 129 healthy adults, 215 with metabolic disorders, 77 with gastric cancer and 86 with colorectal cancer.
What screening looks like today
The mouth-rinse test is not something anyone can order yet.
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Meanwhile, the American Cancer Society recommends several colorectal screening options starting at age 45. Colonoscopy every 10 years is the most thorough.
Annual stool immunochemical tests, multitarget stool DNA tests such as Cologuard every three years, and CT colonography every five years are also accepted.
The National Colorectal Cancer Roundtable puts the current up-to-date screening rate at 65 percent of adults aged 45 and older, still short of the 80 percent goal set by public health groups.
Anyone with ongoing changes in bowel habits, unexplained weight loss, persistent abdominal pain or blood in the stool should talk to a doctor rather than waiting for a newer test to arrive.
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This article is made and published by Mie Hermansen, who may have used AI in the preparation.