Fluoride has been in most American tap water for decades. It’s there to help to prevent tooth decay, especially in children. Scientists and health officials say it’s one of the biggest public health wins of the 20th century.

But lately, fluoride has found itself at the centre of a heated debate, with some people concerned about side effects. Robert F Kennedy Jr, the US Health Secretary, is one of those, but he has long expressed views that conflict with scientific evidence.

We break down the facts about fluoride, explain how the quantities of it in water is safe and tell you what you need to know with Phoebe Hopson, a BBC reporter, and Michelle Roberts, a doctor and health reporter.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 0330 12 33 22 6 Presenter: Hannah Gelbart Producers: Julia Ross-Roy and Emily Horler Editor: Verity Wilde