Naswar, Oral Bacteria, and Cancer: How Smokeless Tobacco Reshapes the Mouth's Microbial World

Naswar — a moist smokeless tobacco product made from tobacco leaf, ash, and various additives — is widely used among men in Khyber Pakhtunkhwa and other parts of Pakistan. Despite its prevalence, its effects on the oral microbiome and cancer biology have been largely understudied. Our lab's research is beginning to paint a clear and concerning picture.

Using 16S rRNA sequencing of oral rinse and buccal swab samples from regular naswar users compared to non-users, we have demonstrated significant shifts in the oral bacterial community. Notably, regular naswar use is associated with a marked decrease in protective commensal organisms such as Streptococcus sanguinis and an enrichment of Fusobacterium nucleatum — a bacterium increasingly recognised as a co-driver of head and neck squamous cell carcinomas.

Fusobacterium nucleatum promotes tumour progression through several mechanisms: it activates E-cadherin signalling pathways that stimulate cancer cell proliferation, suppresses local immune surveillance, and creates a pro-inflammatory microenvironment that facilitates invasion and metastasis. The enrichment of this organism in naswar users with premalignant oral lesions is a particularly alarming finding from our study.

We also measured salivary levels of proinflammatory cytokines IL-6, IL-8, and TNF-α, finding significantly elevated levels in naswar users with dysplastic oral mucosa compared to those without lesions. This immune activation appears to be, at least partly, mediated by the altered microbial communities rather than the chemical carcinogens in tobacco alone.

Our findings advocate for the inclusion of oral microbiome screening as part of early cancer detection programmes in KPK, and support targeted public health messaging about naswar use that goes beyond the chemical toxicology to highlight the microbial disruption it causes. We are now exploring whether probiotic interventions can partially restore normal oral bacterial communities in heavy naswar users.