Inspired and informed by contemporary research within Science and Technology Studies (STS), this essay discusses how social epidemiological research serves to create and produce health inequalities in society. Focusing in particular on how social epidemiology establishes the relationship between socio-economic status and health, it examines how the accumulation of different studies relying on different indicators and measures results in the construction of new facts and generalizations concerning the health of people with a lower socio-economic status. By identifying groups “known to be unhealthy”, the essay presents social epidemiology as participating in the co-production of the social and political infrastructures underlying policy decisions. To increase awareness within social epidemiology of the politics of its own knowledge practices, it concludes by recommending new interdisciplinary collaborations.