The correct reaction to the controversy over potentially contaminated baby milk is over-reaction, such as the withdrawal of all relevant products from sale, a risk expert said this week, writes Aisling Irwin.

The scandal is a classic example of a category of risk in which trust in authorities and companies becomes paramount, the Society for Risk Analysis-Europe heard at its annual meeting in Surrey.

Ortwin Renn, chair of environmental sociology at the University of Stuttgart, said in the opening address to the meeting that food scares are "Pandora's box" scares - invisible threats to one's health or well-being which have delayed effects and affect only a few people at the same time.

Knowledge about these risks is based on information from others rather than on personal experience.

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Professor Renn said: "These risks pose a major demand for trustworthiness in those institutions that provide information and manage the hazard. If trust is lost, people demand immediate actions and assign blame to these institutions even if risks are very small."

He compared the milk controversy with another situation which was dealt with successfully, the poisoning of a small number of aspirin manufactured by Tyranol. "Tyranol took all of its products from all of the shelves in all of the United States. Afterwards people said 'this is a really responsible company'."

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Efforts to reduce risks are suffering because different disciplines with different insights are not talking to each other, he added.