Marie Johnston is a pioneer in the field of health psychology: the discipline that seeks to understand how psychological, behavioural and cultural factors contribute to our physical and mental health. Today an emeritus professor in health psychology at the University of Aberdeen, her career exploring behavioural interventions has shown that even the subtlest shift in how we act can dramatically change our behaviour and lives for the better – whether that’s in an individual recovering from a stroke, or a nation coming to terms with pandemic safety measures, while her work setting up the UK’s first stress management clinic showed why mental health support needed to come out of psychiatric hospitals and into general practice. Marie tells Professor Jim Al-Khalili why she believes the right interventions can be a powerful tool in improving public health, and indeed our healthcare system; and how an accident at the hairdresser's many years ago helped her become more approachable... Produced by Lucy Taylor.