Letters: What cycle helmets can tell us about face masks

Masking the truth

Sir: Matthew Parris is right to laud the importance of embracing the scientific method (‘Why should opinion matter more than science?’, 25 July) to determine the efficacy of face masks. However, his proposed experiment contains a significant oversight — the human factor. That is, how the very wearing of a mask (or a conscious decision not to) may itself result in behaviours that alter transmission risk.