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Some risk factors for asthma

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Since infants and young children spend much of their time in the home and the factors that lead to asthma probably act in early life, the home environment is an obvious place to look for such factors. The authors of recent papers from Australia have concentrated on volatile organic compounds (VOCs) and household heaters.

Household sources of VOCs include solvents, floor adhesive, paint, cleaners, furnishings, polishes, and room fresheners. Exposure has previously been related to asthma and asthmatic symptoms. In Perth (

) a case-control study included 88 cases (children aged 6 months to 3 years who attended the emergency department with asthma) and 104 population controls in the same age group but without asthma. Health status and home environment characteristics were assessed by standardised questionnaire and the concentration of VOCs in air was measured in the home living room soon after the emergency room visit (in winter) and approximately 6 months later (in summer). Controls were monitored at the same times. Measurements were obtained for benzene, toluene, m-xylene, o,p-xylene, ethylbenzene, styrene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1, 4-dichlorobenzene, and total VOCs. Almost all homes contained benzene, toluene, and xylene and VOC concentrations were significantly higher after recent inside painting. Total VOC concentrations were significantly higher in cases than in controls (median total VOCs 78.5 μg/m3v 36.2 μg/m3). After controlling for potential confounding factors a high living room VOC concentration (above the median) was associated with a fourfold increase in risk of asthma and high exposure to benzene with an eightfold increase. Benzene, ethylbenzene, and toluene were the particular VOCs associated with greatest risk. VOC concentrations were significantly related to recent painting, new carpets, new furniture, and smoking indoors.

The combustion products of unvented heaters and cookers include nitrogen dioxide, sulphur dioxide, carbon monoxide, and water vapour, and gas stoves have been associated with an increase in respiratory symptoms in children. In New South Wales (Thorax 2004; 59:741–5) schoolchildren aged 8–11 years were studied by parent completed questionnaire, skin prick testing, and histamine challenge testing. Exposure to fume emitting heaters during the first year of life, but not currently, was associated with increased risk of airway hyperresponsiveness (AHR), recent wheeze, and recent wheeze plus AHR, but not with atopy or doctor diagnosed asthma. The risk of AHR was increased by 47%, of recent wheeze by 44%, and of recent wheeze plus AHR by 108%. The most common types of fume emitting heaters were non-flued gas heaters and wood stoves.

Exposures at home of young children to VOCs and of infants to fume emitting heaters both increase the risk of childhood asthma.

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