Does early exposure to cat or dog protect against later allergy development?

Background It is unknown which factors in modern western society that have caused the current increase in prevalence of allergic diseases. Improved hy giene, smaller families, altered exposure to allergens have been suggested. Objectives To assess the relationship between exposure to pets in early lif e, family size, allergic manifestations and allergic sensitization at 7-9 a nd 12-13 years of age. Methods The prevalence of allergic diseases and various background factors were assessed in 1991 and 1996 by questionnaire studies. In 1991, the study comprised representative samples of children from the Goteborg area on the Swedish west coast (7 years old, n = 1649) and the inland town Kiruna in n orthern Sweden (7-9 years old, n = 832). In 1992, a validation interview an d skin prick test (SPT) were performed in a stratified sub-sample of 3,412 children. In 1996, this subgroup was followed up with identical questions a bout clinical symptoms as in 1991, detailed questions about early pet expos ure were added and SPT performed. Results Children exposed to pets during the first year of life had a lower frequency of allergic rhinitis at 7-9 years of age and of asthma at 12-13 y ears, Children exposed to cat during the first year of lift: were less ofte n SPT positive to cat at 12-13 years. The results were similar when those c hildren were excluded, whose parents had actively decided against pet keepi ng during infancy because of allergy in the family. There was a negative co rrelation between the number of siblings and development of asthma and alle rgic rhinitis. Conclusion Pet exposure during the first year of life and increasing number of siblings were both associated with a lower prevalence of allergic rhini tis and asthma in school children.