The data from the present study revealed that almost half the children aged between 4 and 11 years living in poor neighbourhoods in a large city in the tropical region of Brazil have evidence of infection with Toxocara. Although this infection was associated with enhanced inflammatory markers (eosinophilia, total IgE) and an increased prevalence of sIgE, it appeared to be protective against immediate hypersensitivity reactions in the skin induced by common aeroallergens. This evidence concerns the gene IGHE and infection.