Allergic rhinitis in children: environmental factors

Summary Increasing numbers of patients with allergic rhinitis are being noted on a global scale. Over 90% of Japanese patients with perennial allergic rhinitis show allergic reaction to the mite antigen and major pollen allergens such as Japanese cedar and Japanese cypress, which are carried long distances (> 100 km) by wind and hence can produce substantial harmful effects even in metropolitan areas. This situation is distinct from that in the West, where the most common anemophilous allergen, ragweed, travels much shorter distances of up to only several hundred metres. Environmental factors such as increased antigen, air pollution, diet, intestinal microflora, decreased incidence of infections, smoking, breastfeeding and vaccination may play important roles in the development and manifestation of allergic rhinitis in genetically predisposed subjects. In particular, in newborn infants, who carry the Th2 predominant state, environmental factors may greatly affect the development of balanced production of Th1 and Th2 cytokines. However, the contribution of any environmental factor to the postnatal development of allergic rhinitis has not been sufficiently determined. A better understanding of the processes involved may lead directly to better treatment or cure of allergic rhinitis.