Cats and dogs and the risk of atopy in childhood and adulthood

Background: Exposure to cats and dogs during childhood has been linked to a lower risk of developing allergies. It remains unclear whether this is due to selective avoidance of pets by families with a history of allergies. The effects of pet ownership in adulthood are unknown. Objectives: We sought to assess the association between cat and dog ownership in childhood and early adulthood and the development of atopy in a population-based birth cohort of 1037 subjects. Methods: Ownership of cats or dogs between birth and age 9 years and between the ages of 18 and 32 years was reported. Skin prick tests to common allergens were performed at 13 and 32 years. Results: There was no evidence that families with a history of atopy avoided owning pets. There were significant cat-by-dog interactions for the development of atopy in both childhood and adulthood. Children who had owned both a cat and a dog were less likely to be atopic at age 13 years. Living with only one of these animals was not protective against atopy. Among those who were not atopic by age 13 years, having both a cat and a dog in adulthood was associated with a lower risk of new atopy by age 32 years. This association was only significant among those with a parental history of atopy. These effects were independent of a range of potential confounding factors. Conclusions: There is a synergistic interaction between cat and dog exposure that is associated with a lower risk of developing atopy in childhood and young adulthood. (J Allergy Clin Immunol 2009;424:745-50.)