SKIN-TEST REACTIVITY AND NUMBER OF SIBLINGS

Objective-To investigate the relation between skin test reactivity in children and number of siblings. Design-Cross sectional survey among s chool-children aged 9-11 years. Skin prick tests in the children and s elf completion of written questionnaire by their parents. Subjects-503 0 children in Munich and 2623 children in Leipzig and Halle, Germany. Main outcome measures-Atopic status assessed by skin prick tests. Resu lts-After possible confounders were controlled for, the prevalence of atopic sensitisation decreased linearly with increasing number of sibl ings (odds ratio=0.96 for one sibling, 0.67 for five or more siblings; P=0.005). In atopic children the severity of the skin test reaction a s assessed by the weal size was not associated with the number of sibl ings. Conclusions-Factors directly or indirectly related to the number of siblings may decrease the susceptibility of children to become ato pic. Thus, declining family size may in part contribute to the increas ed prevalence of atopic diseases reported in Western countries over th e past few decades.