IT WOULD be 'quite wrong' to assume that higher levels of outdoor air pollution have caused the rise in cases of asthma, Dr Kenneth Calman, the Government's Chief Medical Officer, said yesterday, writes Celia Hall.

At the launch of his annual report On the State of Public Health 1993, he said: 'Asthma is an allergic response in the lungs caused by a variety of things - indoor and outdoor air pollution, diet and maternal smoking. It is important to get the significance of outdoor air into proportion.'

Two million people in England suffer from asthma and there are 1,600 deaths a year, Dr Calman said, but while the asthma rates have been rising since 1974, death rates have remained stable.

He pointed to the house- dust mite as one cause for the increased incidence of asthma. The mite's habitat has been improved by central heating, closed windows and wall-to-wall carpeting.

He said that people who already had asthma were affected when outdoor pollution was high. 'The question is, is there evidence that air pollution causes it? There is some preliminary evidence but no clear relationship has been shown.

'There are some places with high pollution levels but low levels of asthma. If you banned all cars in central London you would not suddenly see a drop because asthma has all sorts of causes.'

Asthma affects 4 to 6 per cent of children and 4 per cent of adults. The number of GP prescriptions has risen from 14.87 million in 1982 to 29.26 million in 1992.

He welcomed a report from the Medical Research Council's Institute for Environmental Health on air pollution and health, which yesterday recommended a full research programme.