To summarize the principal findings on risk and protective factors for childhood
asthma, we retrieved systematic reviews on these topics in children (aged 1 to 18 years), up to January 2016, through MEDLINE, EMBASE, CINAHL, SCOPUS, and CDSR. A total of 227 studies were searched from databases. Among those, 41 systematic reviews (SRs) were included: 9 focused on prenatal factors, 5 on perinatal factors, and 27 on postnatal factors. Of these 41 SRs, 83% had good methodological quality, as determined by the Assess Systematic Reviews tool. After reviewing all evidence, parental
asthma, prenatal environmental tobacco
smoke, and prematurity (particularly very
preterm birth) are well-established risk factors for childhood
asthma. Current findings do suggest mild-to-moderate causal effects of certain modifiable behaviors or exposures during pregnancy (
maternal weight gain or
obesity, maternal use of
antibiotics or
paracetamol, and maternal stress), the perinatal period (birth by Caesarean delivery), or postnatal life (severe
respiratory syncytial virus infection,
overweight or
obesity, indoor exposure to mold or fungi, and outdoor air pollution) on childhood
asthma, but this suggestive evidence must be confirmed in interventional studies or (if interventions are not feasible) well-designed prospective studies.