A case study examining the relationship between ozone depletion, UV radiation and skin cancer shows how scientific uncertainty is reduced and, through consensus building, translated into certainty in public health messages. Using narrative analysis we examine Canadian consensus statements on the dangers of UV and reconstruct the supporting logical claims and scientific evidence. Though considerable uncertainty remains about the relationship between the environment and skin cancer, both public health messages and the UV-Index formalize uncertainty and risk; concern then shifts from the less-certain, scientific realm into the apparently more-certain arena of public health messages. In this process the distinctions between science and policy become blurred. The case can be interpreted in two ways: as the result of various players acting in their self-interests or as a moral drama based on the importance of simple, clear messages to allow ‘correct’ actions.