Does eczema in infancy cause hay fever, asthma, or both in childhood? Insights from a novel regression model of sibling data

Eczema in infancy might have a causal effect on hay fever in children with and perhaps without asthma. The association of infantile eczema on asthma in children without hay fever, which might be early transient wheeze, is unlikely to be causal or familial. These findings have implications for hay fever prevention.