Definitions
“Current eczema symptoms” was defined as a positive answer to two questions: “Have you had this itchy rash (as defined in a previous question) at any time in the past 12 months?” and “Has this itchy rash at any time affected any of the following places: the folds of the elbows, behind the knees, in front of the ankles, under the buttocks, or around the neck, ears or eyes?”. “Severe eczema symptoms” was defined as symptoms of current eczema being the cause of awakening one or more times per week in the question: “In the past 12 months, how often, on average, have you (has this child) been kept awake at night by this itchy rash? (Never in the past 12 months, less than one night per week, one or more nights per week). “Eczema ever” was defined as a positive answer to: “Have you ever had eczema?”.
“Current wheeze” was defined by a positive answer to the question “Have you (has your child) had wheezing or whistling in the chest in the past 12 months? Current wheeze was used to stratify eczema markers in some of the statistical analyses.
Additionally, adolescents responded to the environmental questionnaire. This included questions on smoking; pet ownership; paracetamol use, truck traffic in the street where adolescents lived; siblings; time spent using screens or watching television; and exercise. Additionally, height and weight were measured at school by fieldworkers in a standardised way according to GAN methods12.Exercise was assessed by the question “How many times a week do you engage in vigorous physical exercise activity long enough to make you breath hard? (Never or occasionally; once or twice per week; three or more times per week)”. Paracetamol intake was surveyed by the question: “In the past 12 months, how often, on average, have you taken paracetamol for fever? (Never; At least once a year; At least once per month)”. Overweight was defined as body mass index above 25.