To systematically search, summarize, and critically appraise the literature to examine whether pet exposure in early life is associated with an increased risk of eczema.
Data Sources and Study Selection
We searched MEDLINE (1950 to June 2006) supplemented by citation lists in retrieved articles and contact with researchers. No language restrictions were imposed.
Cohort studies were sufficiently similar to allow pooled analysis. Meta-analysis was not possible for cross-sectional studies owing to differences in methods and populations.
Main Outcome Measures
Incidence or prevalence of eczema.
Evidence from longitudinal studies showed that previous exposure to cats (pooled odds ratio [OR], 0.76; 95% confidence interval [CI], 0.62-0.92), dogs (pooled OR, 0.68; 95% CI, 0.53-0.87), or “any furry pet” (pooled OR, 0.79; 95% CI, 0.74-0.84) is associated with a lower risk of eczema. However, in the only cohort study adjusted for avoidance behavior, this “protective effect” disappeared (for cats: OR, 0.80; 95% CI, 0.33-1.97). Stratified analysis by family history in 2 birth cohort studies showed that dog exposure was protective in patients with atopic families. For cats, 1 study showed reduced risk in atopic families only; the other study showed no effect. Eight cross-sectional studies evaluated past pet exposure; a protective effect was seen in 3 studies for cat, dog, or any pet; no study demonstrated an increased risk.
There was no clear evidence that early pet exposure is associated with increased risks of subsequent eczema. We found some evidence of a possible protective effect of early pet exposure, but this might be explained by avoidance behavior in high-risk families.