Atopic dermatitis will be determined through the ISAAC core questions on atopic dermatitis, which are based on a list of major and minor criteria widely applied in clinical studies. 8, 30, 31 As eczema is probably more readily confirmed by objective tests than either asthma or rhinitis, patients will be considered to have definite atopic dermatitis if between age 5 and 6 years they report ever having an itchy rash that comes and goes for at least 6 months, and being diagnosed with eczema by a physician. 30, 31 Probable atopic dermatitis will be defined as one of the two above criteria.