Science deniers question scientific milestones and spread misinformation, contradicting decades of scientific endeavour. Advocates for science need effective rebuttal strategies and are concerned about backfire effects in public debates. We conducted six experiments to assess how to mitigate the influence of a denier on the audience. An internal meta-analysis across all the experiments revealed that not responding to science deniers has a negative effect on attitudes towards behaviours favoured by science (for example, vaccination) and intentions to perform these behaviours. Providing the facts about the topic or uncovering the rhetorical techniques typical for denialism had positive effects. We found no evidence that complex combinations of topic and technique rebuttals are more effective than single strategies, nor that rebutting science denialism in public discussions backfires, not even in vulnerable groups (for example, US conservatives). As science deniers use the same rhetoric across domains, uncovering their rhetorical techniques is an effective and economic addition to the advocates' toolbox.