BACKGROUND: In adults, there is limited information on tolerance to cat, which may be reflected by high IgG4 without IgE sensitization. Early exposure to cat may play a critical role. OBJECTIVE: The aim was to assess among adults the association of Fel d 1 IgG4, Fel d 1 IgE, skin prick test (SPT) response to cat and pet-related symptoms in relation to exposure to cat considering the period of exposure. METHODS: SPT response to cat, specific IgE and IgG4 to Fel d 1 were assessed in 167 asthmatics recruited in chest clinics (40 years of age in average) from the French Epidemiological study on the Genetics and Environment of Asthma (EGEA). Childhood and/or current exposure to cat were studied retrospectively. RESULTS: IgG4 was higher in relation to current cat exposure (0.53 vs. 0.09 ng/mL; P<0.001) and higher in women than in men. The period of cat exposure was significantly related to Fel d 1 IgE, the IgE/IgG4 pattern and cat weal size. The lowest values of Fel d 1 IgE, cat weal size, pet-related nasal or respiratory symptoms were observed in those with both childhood and current exposure as well as the highest proportion of the IgE-/IgG4+ pattern observed in 1.4%, 4.0%, 38.1% and 12.5% of those with -/-, +/-, +/+, -/+ childhood/current exposure, respectively. CONCLUSIONS: Adult asthmatics exposed to cats since childhood present an immunologic pattern with high IgG4 and low IgE. Continuous exposure may maintain a state of immunological tolerance to cat.