The impact of risk communication depends upon a complex interaction between the characteristics of the audience, the source of the message, and its content. Audience perception of risk is influenced by demographic factors (e.g. age, gender), personality profile, past experience, and ideological orientation. It is also affected by cognitive biases (e.g. unrealistic optimism) and lay 'mental models' of the hazard. For food hazards, the important dimensions of risk are controllability, novelty and naturalness. The source must be trusted for a risk message to be effective. Trust is associated with believing the source is expert, unbiased, disinterested, and not sensationalising. To maximise impact, risk communications must have a content which triggers attention, achieves comprehension and can influence decision-making. It must be unambiguous, definitive and easily interpretable--rarely achievable particularly when risk is shrouded in scientific uncertainty. Risk messages initiate social processes of amplification and attenuation, consequently their ramifications are rarely controllable.