Age-dependent tendency to become sensitized to other classes of aeroallergens in atopic asthmatic children Michela Silvestri, PhD; Giovanni A Rossi, MD; Simonetta Cozzani, MD*; Grazia Pulvirenti, MD*; and Lilia Fasce, MD* Background: Several longitudinal studies report that allergic sensitization in- creases with age from childhood to adulthood. Objective: To evaluate whether an age-dependent tendency to become sensitized to new classes of allergens is present in atopic children, we studied retrospectively the changes in allergic sensitization in 165 asthmatic patients, monosensitized (ie, sensitized to only one class of allergens) in the first survey. Methods: All the children (18 months to 8 years at enrollment), attended our outpatient clinics twice, at time intervals ranging from 2 to 10 years. On each visit, sensitization to house dust mites, pollens, animal danders, and molds was deter- mined by skin prick test. Results: We found that 43.6% (n = 72) of the patients became polysensitized on the second survey. According to age on first survey, the patients were further divided into two age groups: (1) group 1 = 18 months to 5 years old (n = 98) and (2) group 2 = 5 to 8 years (n = 67). The transition from monosensitization to polysensitization observed in the entire population was present in both groups: 47 (47.9%) of the 98 children in group 1 and 25 (37.3%) of the 67 children in group 2 showed to be sensitized to more classes of allergens, as compared with first survey. Both in the whole population and in the two age subgroups, the changes in the frequency of monosensitization between the two evaluations were time-dependent ( P  .05, each Chi 2 ). Finally, to investigate whether monosensitization to a specific class of allergens could favor the development of polysensitization, we evaluated the frequency of polysensitization in the second survey in patients originally monosensitized to house dust mites or to pollens. We found that of the 130 patients originally monosensitized to house dust mites, 59 became polysensitized (45.4%), while of the 28 patients originally monosensitized to pollens, 9 became polysensitized (32.1%) (P  .1). Similar results were obtained when patients were divided into age groups. Conclusion: These data demonstrate that (1) monosensitized children are likely to become polysensitized and (2) house dust mite sensitization and, at a lower degree, pollen sensitization, apparently seem to play a “triggering” role in the development of polysensitization, since a high proportion of children originally monosensitized to house dust mites or to pollens became polysensitized. Ann Allergy Asthma Immunol 1999;83:335–340. INTRODUCTION Over the last 20 to 30 years, the prev- alence of atopic diseases has increased considerably in developed countries. Population-based studies showed this was true at least in children and young adults. 1–7 Atopic diseases are complex and multifactorial since their develop- ment and phenotypic expression de- pend on interaction between genetic factors, environmental exposure to al- lergens, and nonspecific adjuvant factors, such as tobacco smoking, air pollution, and infections. 8 The rela- tive roles of genetic and environmen- tal factors in allergic diseases have not been completely clarified yet. 9 –12 Subjects genetically prone to sensiti- zation are likely to require prolonged exposure to allergens before devel- oping respiratory allergic symptoms. In this context, several longitudinal studies in birth cohorts and in sub- jects with asthma report that allergic sensitization persists 13 and increases with age from childhood to adult- hood, reaching its peak in early adulthood. 14 –16 Although some fac- tors facilitating the development of allergy have been identified, 17–21 the development of allergic sensitization in children and the factors that may influence sensitization to one rather than to more different types of aller- gens are still not completely known. Specifically, little is known about the longitudinal intraindividual change in number and type of specific aller- gens from early childhood to adoles- cence. In this context, a previous study 22 reported that the percentage of children sensitized to only one class of allergens decreased with age of the subjects compared with poly- sensitized subjects. Particularly, a more pronounced decrease in the fre- quency of monosensitization was ob- served in children younger than 7 years. 22 To the best of our knowl- edge, no study has been published to date evaluating how and to what ex- tent monosensitization varies with time. The aim of this study was therefore to investigate the time-de- pendent changes in sensitization to different airborne allergens in a sam- ple population of monosensitized preschool and school children. From the Pulmonary Division, G. Gaslini In- stitute and * Pediatric Department, University of Genoa, Genoa, Italy. Supported by Grant “Ricerca Finalizzata Farmacogenetica, from Ministero della Sanita `, Rome, Italy. Received for publication July 24, 1998. Accepted for publication in revised form May 8, 1999. VOLUME 83, OCTOBER, 1999 335