Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 16 2 2017 05 07 82 91 EN Zahra Alizadeh Immunology, Asthma and Allergy Research Institute, Tehran University of Medical Sciences, Tehran, Iran Esmaeil Mortaz Clinical Tuberculosis and Epidemiology Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran AND Department of Immunology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran Ian. Adcock Airway Disease Section, National Heart and Lung Institute, Imperial College London, London, UK Mostafa Moin Immunology, Asthma and Allergy Research Institute, Tehran University of Medical Sciences, Tehran, Iran 2016 06 20 2016 11 07 Asthma is a complex, heterogeneous and chronic airway inflammatory disease with different clinical phenotypes caused by diverse triggers and pathophysiological mechanisms. Asthma heritability has been established in many genetic studies but it is evident that only genetic elements are not responsible for the development of asthma. Increasing rate of asthma incidence during past decades has implicated the role of epigenetics in development of asthma. Environmental factors perform as initiator signals through epigenetic mechanisms. Three epigenetic mechanisms have been identified, including DNA methylation, histone modifications, and small noncoding RNAs. These mechanisms regulate the immune responses and inflammatory genes expression in asthma and allergy. This review explains the role of epigenetic modifications in controlling Th2 response and IgE production in asthma and also briefly overviews the role of environmental factors such as pollutions, allergens, prenatal exposures and diet in developing asthma. Recognizing environmental risk factors and their effects on epigenetic mechanisms would be of great interest for prognostic and preventive aspect in treatment of asthma.  https://ijaai.tums.ac.ir/index.php/ijaai/article/view/975 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/975/718