Background Synergistic role of exposure to cats, dogs, and farm animals during infancy on the risk of childhood asthma and allergy remains unknown.

Objectives To investigate independent and synergistic associations between exposure to indoor pets and farm animals during infancy and the risk of asthma and allergy by age 5.

Methods We studied 3781 children participating in the Finnish Type 1 Diabetes Prediction and Prevention (DIPP) Nutrition Study. At age 5, a validated version of the International Study of Asthma and Allergies in Childhood questionnaire was administered to collect information on asthma and allergic disease, and exposure to indoor pets and farm animals during the first year of life. Allergen‐specific IgE antibodies were analyzed from serum samples. Statistical analyses employed Cox proportional hazards and logistic regression.

Results Having a dog in the house was inversely associated with the risk of asthma (HR 0.60; 95% CI, 0.38‐0.96), allergic rhinitis (OR 0.72; 95% CI, 0.53‐0.97), and atopic sensitization (OR 0.77; 95% CI, 0.63‐0.96). Having a cat was associated with a decreased risk of atopic eczema (OR 0.68; 95% CI, 0.51‐0.92). Farm animals were neither independently nor in synergy with indoor pets associated with the outcomes.