The assertion in your Editorial “Don't believe the hype” (Nature 424, 237; 2003), that new toxicology data on nanomaterials and more public debate on their risks will extinguish the hype surrounding nanotechnology, is unlikely to be correct. Lessons learnt from past controversies suggest that what is actually needed is understanding of what the public perceives to be the risks of nanotechnology.

Collection of scientific data and facts on potential hazards does little to calm the fears of the public, as experiences of silicone breast implants and Bt corn demonstrate. Even scientific evidence showing that there is little or no harm from a particular technology does not put an end to public controversy. It is public attitudes and reactions to perceived, not actual, risks that tip the balance of public acceptance or rejection of new technologies. Why is this so?

Statistics about risks — as assessed by scientific methods — do not necessarily guide the public towards rational decisions (P. Slovic, Science 236, 280–285; 1987). Slovic and his colleagues have shown over the past three decades that non-technical people tend to overestimate the risks of activities that are unfamiliar to them, that may threaten future generations, and that have vivid historical associations, such as Three Mile Island or Chernobyl.

The nanotechnology community is underestimating the importance of perceived risks — and the distinction between these and real risks — and their implications for progress.

In 2002, the US National Nanotechnology Initiative awarded only $280,000 — 0.04% of its budget of $697 million, to study the social and ethical implications of nanotechnology. None of this money was allocated to studying risk perception.

The longer the nanotechnology community waits to address public concerns, the more entrenched risk perception will become in the public's minds. It is up to us to take notice and assess funds accordingly.