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Australia, like many developed nations, has more asthma than poorer nations. A study compared children living in Hong Kong, who have a higher rate of asthma, with children living in nearby Guangzhou and in Beijing. Cooking with gas, foam pillows and damp housing increased the risk of asthma. Asthma varies around the world. Australia, like many developed nations, has quite a lot of asthma, whereas people in poorer nations have a lower risk. Environmental factors, such as mothers smoking during pregnancy and not being exposed to virus infections in the first year of life, are known to increase the risk of asthma but the picture is still far from complete. One way of discovering more is to compare genetically similar populations living in different situations. A Hong Kong study compared Chinese children living in Hong Kong, who have a higher rate of asthma, with children living in nearby Guangzhou and in Beijing far to the north. Hundreds of 10-year-old children in the three areas were compared. The main risk factors which emerged were cooking with gas, foam pillows and damp housing. Fruit and vegetables were protective as was attendance at day care and having more brothers and sisters. The gas and foam pillows may relate to hydrocarbons in the air - which would reinforce Western Australian findings linking volatile organic compounds in indoor air with asthma. The protective nature of day care and siblings almost certainly relates to early exposure to viral infections. This early exposure may distract immature immune systems from developing allergic tendencies.
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