<p>Understanding how modifiable cancer risk factors change across the life course is crucial for evidence-based prevention. However, surveillance of lifestyle factors often relies on cross-sectional studies, unable to capture within-person patterns across the life course. Longitudinal studies assessing long-term exposure patterns are scarce. Within the Generations Study, a prospective cohort of &gt; 113,700 UK women (median recruitment age: 48.4 years; range: 16–102) recruited between 2003 and 2009, we explored life course trajectories of modifiable cancer risk factors, leveraging up to six self-reported exposure measurements collected retrospectively and prospectively. Linear mixed-effects models with natural cubic splines for age were fitted for alcohol consumption, smoking, physical activity and body mass index (BMI). Mean velocity curves were derived from differentiated spline curves. Interactions between age and birth cohort assessed generational differences. Each risk factor showed distinct, nonlinear patterns in the level and rate of change across the life course. Alcohol consumption, smoking and physical activity peaked in late adolescence, whilst BMI increased with age, peaking in the late 60s. Younger cohorts (born 1960–2003) exhibited progressively higher BMI trajectories and earlier peaks in alcohol consumption and smoking intensity compared to older cohorts (born 1908–1959). Modifiable cancer risk factor exposure varied throughout life, highlighting the importance of repeated exposure measurements to capture these patterns. Our findings revealed key life stages for behavioural transitions. This insight can guide targeted prevention and intervention efforts.</p>