AbstractBackgroundFew studies have simultaneously addressed the importance of age of onset and persistence of eczema for the subsequent development of asthma and hay fever, particularly into early adulthood.MethodsA high‐risk birth cohort was recruited comprising 620 infants, who were then followed up frequently until 2 years of age, annually from age 3 to 7, then at 12 and 18 years, to document any episodes of eczema, current asthma, and hay fever. The generalized estimation equation technique was used to examine asthma and hay fever outcomes at 6 (n = 325), 12 (n = 248) and 18 (n = 240) years, when there was consistency of associations across the follow‐ups.ResultsVery early‐onset persistent (onset <6 months, still present from 2 to 5 years) eczema was related to current asthma (adjusted OR = 3.2 [95% CI = 1.7–6.1]), as was very early‐onset remitting eczema (onset <6 months but not present from 2–5 years, OR = 2.7, 95% CI = 1.0–7.2) and early‐onset persistent eczema (onset from 6–24 months, OR = 2.3, 95% CI = 1.2–4.7). Late‐onset eczema (commenced from 2–5 years) was associated with increased risk of asthma at 12 years (OR = 3.0, 95% CI=1.1–8.2) but not at age 6 years. Only very early‐onset persistent eczema was associated with increased risk of hay fever (aOR = 2.4, 95% CI = 1.4–4.1).Conclusion and clinical relevanceEczema which commences in early infancy and persists into toddler years is strongly associated with asthma, and to a lesser extent hay fever, in high‐risk children. If these associations are causal, prevention of early‐life eczema might reduce the risk of respiratory allergy.