Public policy aimed at preventing undesired phenomena has increasingly sought to engage representatives of the target population. Little is known, however, about how power dynamics function to shape the processes and outcomes of risk governance engagement interventions. In order to study the ways in which, and the extent to which, power differentials can be reduced in participatory health promotion initiatives, we develop a conceptual framework synthetising theories of participatory action, phenomenology and governmentality. Based on the empirical research into youth participation in the EU project CO-CREATE, involving 15–19-year-old adolescents in five European countries (2019–2021), we show that diverse forms of knowledge may become available in engagement interventions. We analyse the use and relative inclusion and exclusion of these different forms of knowledge in terms of a three-level framework of different depths of democratisation in participatory health promotion: risk management, risk definition and risk negotiation. Advanced democratisation can only be achieved if risk negotiation is carried out in ways which embrace and encourage a range of different, and potentially conflicting forms of knowing.