What is it?

When fossil fuels are burned they produce certain gases, one of which is known as nitrogen dioxide (NO2). Thus cars produce NO2 - and so do gas cookers and gas central heating boilers. Most cookers and boilers are vented to the outside with a flue - but small quantities of NO2 may still be found in homes with gas appliances. This is especially so in kitchens.

Why might it matter?

High concentrations of NO2 are irritating to the lining of the lungs. Thus people who encounter such concentrations - generally in factories but occasionally from heavy traffic - may cough and become a little breathless. Some researchers have suggested that women who use gas cookers have slightly lower lung function than women who do not; men don't seem to be affected in the same way which may reflect who does the cooking……

All this is speculative - and especially because NO2 concentrations in most homes are likely to be very low. We thought, however, that it would be important to study this in Ashford.

What did we do?

Around two months after each child was born, we left a small plastic tube in the living room of their home. This is known as a 'diffusion tube' and over a fortnight it measures the average level of NO2 in the air. We left it in the living room (rather than the kitchen) because we guessed that small children were more likely to spend time there. We attached the tube to a wall, about six feet from the floor to keep it away from prying fingers!

After two weeks we put a cap on the tube and sent it to the Kent County Council laboratories for analysis.

What did we find in Ashford?

On average the levels of nitrogen dioxide in the Ashford living rooms were very low (about 8 parts per billion) and only one or two would give cause for alarm. Homes with gas cookers had higher levels but the differences were very small

Homes with gas cookers had slightly higher levels of nitrogen dioxide in the living room number of homes in the Ashford study average nitrogen dioxide level (parts per billion) in the living room

We would have found higher levels if we had made the measurements in kitchens. However we reasoned that babies spend more time in the living room and that levels there would be more relevant to them.

We found no relationship between the levels of nitrogen dioxide in the living room and whether or not the Ashford children had any wheezing before their first birthdays.

Levels of nitrogen dioxide in the living room did not affect children's wheezing average level of nitrogen dioxide in the living room how often did the children wheeze before their first birthday?

We are of course interested in cigarette smoking because the fumes are quite irritating to the airways of small babies. There is evidence from elsewhere that young children wheeze more often when there is a smoker in the home. We were also interested in smoking during pregnancy and wanted to know whether this was especially important in the development of asthma.

What did we do?

Each time we interview mothers we ask them whether they smoke - or whether anybody else in the home does. If so we ask them how many cigarettes are smoked each day.

When we did this during the Ashford mothers' pregnancies we collected urine samples as well. In these we measured levels of cotinine. Cotinine is a breakdown product of nicotine and this is a good way of deciding whether someone really is a smoker or not. As it happened we didn't need to have bothered. In almost all cases the results of the urine measurements were almost exactly what we would have expected from the answers to our questionnaires.

What did we find?

In 39% of families there was at least one adult who smoked cigarettes. 19% of mothers reported smoking during pregnancy. Exposure to cigarette smoke increases the risk of the child wheezing.

Young children whose parents smoke were nearly twice as likely to wheeze - this is particularly true if the mother smoked risk