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Objectives The incidence of oral cancer has been rapidly increasing in India, calling for evidence contributing to a deeper understanding of its determinants. Although disadvantageous life‐course socioeconomic position (SEP) is independently associated with the risk of these cancers, the explanatory mechanisms remain unclear. Possible pathways may be better understood by testing which life‐course model most influences oral cancer risk. We estimated the association between life‐course SEP and oral cancer risk under three life‐course models: critical period, accumulation and social mobility. Methods We recruited incident oral cancer cases (N = 350) and controls (N = 371) frequency‐matched by age and sex from two main referral hospitals in Kozhikode, Kerala, India, between 2008 and 2012. We collected information on childhood (0‐16 years), early adulthood (17‐30 years) and late adulthood (above 30 years) SEP and behavioural factors along the life span using interviews and a life‐grid technique. Odds ratios (OR) and 95% confidence intervals (CI) were estimated for the association between life‐course SEP and oral cancer risk using inverse probability weighted marginal structural models. Results Relative to an advantageous SEP in childhood and early adulthood, a disadvantageous SEP was associated with oral cancer risk [(OR = 2.76, 95% CI: 1.99, 3.81) and (OR = 1.84, 95% CI: 1.21, 2.79), respectively]. In addition, participants who were in a disadvantageous (vs advantageous) SEP during all three periods of life had an increased oral cancer risk (OR = 4.86, 95% CI: 2.61, 9.06). The childhood to early adulthood social mobility model and overall life‐course trajectories indicated strong influence of exposure to disadvantageous SEP in childhood on the risk for oral cancer. Conclusions Using novel approaches to existing methods, our study provides empirical evidence that disadvantageous childhood SEP is critical for oral cancer risk in this population from Kerala, India.

International audience; Some studies suggest that periodontal diseases increase the risk of oral cancer, but contradictory results also exist. Inadequate control of confounders, including life course exposures, may have influenced prior findings. We estimate the extent to which high levels of periodontal diseases, measured by gingival inflammation and recession, are associated with oral cancer risk using a comprehensive subset of potential confounders and applying a stringent adjustment approach. In a hospital-based case-control study, incident oral cancer cases (N = 350) were recruited from two major referral hospitals in Kerala, South India, from 2008 to 2012. Controls (N = 371), frequency-matched by age and sex, were recruited from clinics at the same hospitals. Structured interviews collected information on several domains of exposure via a detailed life course questionnaire. Periodontal diseases, as measured by gingival inflammation and gingival recession, were evaluated visually by qualified dentists following a detailed protocol. The relationship between periodontal diseases and oral cancer risk was assessed by unconditional logistic regression using a stringent empirical selection of potential confounders corresponding to a 1% change-in-estimates. Generalized gingival recession was significantly associated with oral cancer risk (Odds Ratio = 1.83, 95% Confidence Interval: 1.10-3.04). No significant association was observed between gingival inflammation and oral cancer. Our findings support the hypothesis that high levels of periodontal diseases increase the risk of oral cancer.