Cat exposure during childhood has been shown to increase the risk of developing cat sensitization, while the effect of cat exposure in adulthood has not yet been established.

To evaluate new-onset sensitization to cat in adulthood in relation to changes in cat keeping.

A total of 6292 European Community Respiratory Health Survey I (ECRHS I) participants aged 20 to 44 years from 28 European centers, who were not sensitized to cat, were reevaluated 9 years later in ECRHS II. Present and past cat ownership and total and specific IgE levels were assessed in both surveys. Allergen-specific sensitization was defined as a specific serum IgE level of 0.35 kU/L or more.

A total of 4468 subjects did not have a cat in ECRHS I or ECRHS II, 473 had a cat only at baseline, 651 acquired a cat during the follow-up, and 700 had a cat at both evaluations. Two hundred thirty-one subjects (3.7%) became sensitized to cat. In a 2-level multivariable Poisson regression model, cat acquisition during follow-up was significantly associated with new-onset cat sensitization (relative risk = 1.85, 95% CI 1.23-2.78) when compared with those without a cat at both surveys. Preexisting sensitization to other allergens, a history of asthma, nasal allergies and eczema, and high total IgE level were also significant risk factors for developing cat sensitization, while cat ownership in childhood was a significant protective factor.

Our data support that acquiring a cat in adulthood nearly doubles the risk of developing cat sensitization. Hence, cat avoidance should be considered in adults, especially in those sensitized to other allergens and reporting a history of allergic diseases.