In applied health care research, an essentialised notion of culture is often used when studying ethnic disparities in health and health care access between the majority populations of Western countries and migrants, with ethnic backgrounds that differ from majority population. This notion of culture, however, is considered highly problematic in anthropology and ethnic studies. Therefore, in our research on Dutch illness certification practices, we employed a dynamic conceptualisation of culture. Our research shows that, in practice, when clients fail to meet the implicit norms of this practice, doctors ascribe this nonconformity differently when the client is a migrant than when he or she is a Dutch client. More specifically, when migrants fail to meet the norms, doctors are inclined to automatically ascribe this nonconformity to the assumed cultural background of the client. Consequently, these doctors feel less able to use the tools they normally use to coach their clients. This, in turn, results in more problematic and longer reintegration trajectories for migrants in comparison to Dutch clients in similar circumstances. In other words, framing the problems of migrants in terms of culture results in greater sick leave rates for migrants than for Dutch people. Clearly, culturalistic perspectives on ethnic differences have negative consequences. We therefore implore the application of a dynamic notion of culture in applied research.