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This thesis studied environmental factors in relation to asthma and respiratory symptoms among schoolchildren in two countries. In Sweden, 1014 pupils (5-14 year) in 8 schools participated. Wheeze was reported by 7.8%, current asthma by 5.9%, doctor-diagnosed asthma by 7.7%, cat allergy by 6.8% and dog allergy by 4.8%. Current asthma was less common among those consuming more fresh milk and fish. Doctor-diagnosed asthma was less common among those consuming olive oil. Cat, dog and horse allergens were common in settled dust and related to respiratory symptoms. Pupils consuming butter and fresh milk had less respiratory symptoms in relation to allergen exposure. In schools with increased levels of microbial volatile organic compounds and selected plasticizers (Texanol and TXIB) asthma and respiratory symptoms were more common.

In Korea, 2365 pupils (9-11 year) in 12 schools participated (96%). In total, wheeze was reported by 8.0%, current asthma by 5.7%, doctor-diagnosed asthma by 5.4%, cat allergy by 2.6% and dog allergy by 4.9%. Contamination of dog and mite (Dermatophagoides farinae) allergen was common while cat allergen was uncommon. Remodelling, changing floor and building dampness at home were positively associated with asthma and respiratory symptoms. The strongest associations were found for floor dampness. Indoor/outdoor concentration of NO₂, formaldehyde and ultrafine particles (UFP) at schools were positively associated with asthma and respiratory symptoms.

When comparing Sweden and Korea, Korean pupils had more breathlessness and asthma but reported less cat and pollen allergy. Swedish schools had CO₂-levels below 1000 ppm, while most Korean schools exceeded this standard. Since both home and school environment may affect pupil’s asthma and respiratory symptoms, air quality should be an important health issue. Moreover, changes in dietary habits may be beneficial to decrease asthma and allergies. Furthermore, interaction between diet and environment needs to be further investigated.