Different allergic diseases are closely associated with the unbalanced type 2 immune response, namely allergic asthma, atopic dermatitis, food allergies, hay fever, etc. Although the pathogenesis of asthma and related allergic diseases is very complex and far from thorough understanding, enhanced oxidation of SCN− by heme peroxidases and, in particular, activation of EPO are under discussion to contribute to disease development. The gene discussed is EPO; the disease is allergic disease.