When the Tongue Tells a Deeper Story: Microbial Clues to Colorectal Cancer
Can a simple tongue check reveal insights into cancer?
Colorectal cancer (CRC) remains one of the leading causes of cancer-related death worldwide. In modern medicine, diagnosis and monitoring rely on colonoscopy, imaging, and molecular tests. Yet researchers are increasingly interested in whether simple, non-invasive physical signs might also reflect underlying disease. One such sign comes from an often-overlooked organ: the tongue.
A 2025 open-access study published in BMC Microbiology explores how tongue appearance and tongue-coating bacteria are associated with colorectal cancer. By combining concepts from Traditional Chinese Medicine (TCM) with modern microbiome sequencing, the study offers a fresh perspective on how oral health, microbes, and cancer may be connected.
Why the tongue matters in health assessment
In Traditional Chinese Medicine, tongue diagnosis has been used for centuries to evaluate internal health. Practitioners observe tongue color, coating, texture, and moisture as indicators of physiological imbalance. Historically, this approach has been criticized for its subjectivity.
Advances in digital tongue imaging and microbiome analysis are now helping to translate this traditional practice into measurable biological data. At the same time, growing evidence suggests that oral bacteria can influence gut health, and in some cases contribute to inflammation and cancer development. This makes the tongue a promising window into systemic disease.
What did the researchers do?
The study involved 59 patients diagnosed with colorectal cancer. For each participant, the researchers conducted:
Standardized digital tongue imaging
Collection of tongue-coating samples
Full-length 16S rRNA sequencing, a high-resolution method for identifying bacterial species
These findings were then analyzed in relation to clinical factors such as age, sex, cancer stage, and tumor location.
Four tongue patterns commonly seen in CRC patients
The analysis identified four recurring tongue patterns among patients with colorectal cancer:
Yellow greasy coating
White greasy coating
Petechiae (small red or purple spots on the tongue)
Red tongue with little or no coating
These patterns were not random. Several showed meaningful associations with clinical characteristics, suggesting that tongue appearance may reflect deeper biological changes linked to cancer.
The tongue-coating microbiome: key bacterial players
Microbiome analysis revealed that Streptococcus and Neisseria were the most abundant bacterial genera on the tongues of CRC patients. More importantly, specific bacteria were closely associated with particular tongue patterns:
Alloprevotella rava was strongly linked to yellow greasy coatings
Prevotella intermedia, a well-known periodontal pathogen, was associated with white greasy coatings
This is clinically relevant because Prevotella intermedia has previously been implicated in colorectal cancer progression and tumor invasiveness, highlighting a possible biological bridge between oral infection and intestinal cancer.
Age-related differences in tongue microbiota
Age emerged as one of the strongest factors influencing tongue-coating bacteria.
In patients younger than 62 years, Streptococcus parasanguinis was more prevalent
In patients 62 years and older, Prevotella sp. 000163055 became dominant
These age-related shifts suggest that tongue microbiome profiles may act as age-specific microbial signatures in colorectal cancer.
Why these findings matter
The study does not propose tongue diagnosis as a replacement for established CRC screening tools such as colonoscopy. However, it highlights several promising possibilities:
Tongue appearance may reflect systemic biological changes associated with cancer
Tongue-coating bacteria could serve as non-invasive microbial biomarkers
Integrating traditional diagnostic concepts with modern microbiology may support earlier risk assessment and disease monitoring
In the long term, this approach could contribute to more personalized and preventive strategies in colorectal cancer care.
Study limitations and future directions
The authors acknowledge several limitations:
The absence of a healthy control group
A relatively small sample size from a single geographic region
Observational findings that show association rather than causation
Future multi-center and longitudinal studies, especially those including healthy populations, will be essential to validate and expand these results.
Take-home message
By bridging traditional medical observation with cutting-edge microbiome science, this study suggests that the tongue often overlooked in modern diagnostics may carry valuable biological signals related to colorectal cancer.
While further research is needed, the findings remind us that important clues to disease may be visible in plain sight.
Original article reference
Zheng W, Wu Y, Chu J, et al. Characteristics of tongue images and tongue coating bacteria in patients with colorectal cancer. BMC Microbiology. 2025;25:285.
DOI: https://doi.org/10.1186/s12866-025-04014-3