The role of furry pets in eczema: a systematic review.
OBJECTIVE
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.


METHODS
We searched MEDLINE (1950 to June 2006) supplemented by citation lists in retrieved articles and contact with researchers. No language restrictions were imposed.


METHODS
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.


METHODS
Incidence or prevalence of eczema.


RESULTS
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.


CONCLUSIONS
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.
Langan
Sinéad M
SM
MRCP, Centre of Evidence-based Dermatology, Queen's Medical Centre, Nottingham NG7 2UH, England. sinead.langan@nottingham.ac.uk
Flohr
Carsten
C
Williams
Hywel C
HC
D000818:Animals; D000829:Animals, Domestic; D001362:Avoidance Learning; D002415:Cats; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D004285:Dogs; D004485:Eczema / Q000453:epidemiology / Q000209:etiology* / Q000517:prevention & control; D004781:Environmental Exposure; D006197:Hair; D006801:Humans; D015994:Incidence; D015995:Prevalence; D018570:Risk Assessment