We can't be 100% sure face masks work – but that shouldn't stop us wearing them | Trish Greenhalgh

Public health experts like me know the only conclusive trial of masks will come from them being rolled out in the real world

• Trish Greenhalgh is a professor of primary care health sciences at Oxford University
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Despite disagreement among scientists, we will soon have to wear cloth face coverings on public transport. The policy could be extended to places such as shops where social distancing is difficult.

Passions run high on this issue. I have some sympathy with the person who demanded that scientists should be locked in a room and not let out till they agree the facts. Except that this debate is as much about values as facts.