Does exposure to dogs and cats in the first year of life influence the development of allergic sensitization?

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Abstract
The goal of the review is to place studies published after 1 June 2002, concerning the relationship between early life exposure to cats and dogs and the later development of allergy, within the context of the effects of other environmental exposures on allergic disease. Most of the recent studies have shown that exposure to cats and dogs early in infancy reduces the prevalence of allergic sensitization or allergic disease later in childhood. While this general trend is relatively consistent, there are differences in specific findings between studies, such as the effect of parental allergies. Other studies suggest that the association between cat and dog exposure and a lower risk of allergy is due to either differences in other environmental exposures or to genetic differences between exposed and non-exposed children. It is impossible to directly compare the results from all of these studies since there are often important differences in racial/ethnic backgrounds of the children, climate, housing conditions, and the family and social customs of those enrolled in different studies. The risk of a child developing any form of allergy appears to depend upon many factors including a child's genetic constitution, early environmental exposure to allergens and to other agents which interact with the immune system, and to allergen exposure later in life. It appears that exposure to something that is increased in homes with cats or dogs reduces the risk of allergic sensitization.