Conspiracy theories might be entertaining but they can also be dangerous. Sadly, what often starts off as a bit of fun can turn sour quite quickly – even if it’s laughing about the idea that Rihanna or Katy Perry are part of the Illuminati. We find out how.

This episode delves into some of the psychology behind what makes conspiracy theories dangerous. It also explores the relationship between conspiracy theories and the radicalisation of extremists. And we find out the best ways to talk to people who believe in conspiracy theories.

Psychologist Steve Lewandowsky tells us there is a strong link between people who endorse conspiracy theories and reject climate science. What makes this dangerous is the way that conspiracy theories are used by climate change deniers to justify not acting to reduce carbon emissions.

We also find out more about the links between conspiracy theories and extremism. Political scientist Eirikur Bergmann tells us how populist politicians use conspiracy theories to their advantage, particularly one called the Great Replacement theory. This is the idea that white people in the west are at threat of invasion and being replaced by non-white immigrants.

We also learn how to engage with conspiracy theorists and how difficult it is to convince hardline believers that they are wrong. Psychologist Karen Douglas tells us that it's easier to inoculate people against believing in conspiracy theories in the first place.

And anthropologist Ela Drazkiewicz shares insights from her research into attitudes toward HPV vaccination in Ireland. She explains how mistrust of the health authorities led to a dramatic 30% fall in vaccination uptake between 2014 and 2017. But she also offers hope, describing how the Irish health service managed to turn this around and restore trust in the vaccine.

The Anthill podcast is produced by Annabel Bligh and Gemma Ware for The Conversation. Sound design is by Eloise Stevens, with original music from Neeta Sarl and audio from Epidemic Sound. Thanks to City, University of London, for letting us use their studios. Special thanks to Clare Birchall, Michael Butter and Peter Knight who helped bring this podcast into being, and to the COST Action COMPACT for funding it.