Numerous studies have investigated trends in the occurrence of allergic disorders with recent reports showing that the rate of immediate allergic diseases appears to have doubled over the last 15-20 years. Increases in the number of allergic patients have been reported in countries all over the world. As Thalayasingam and Lee [1] pointed out in the previous issue of this journal, the prevalence of asthma is different in every country. The common environmental risk factors for allergic diseases, especially bronchial asthma, are air pollution, environmental tobacco smoke, nutrition, allergen exposure, family size, infection and hygiene. However, much controversy surrounds the role that each of these risk factors play in the development of allergies. Isolating the effects of environmental risk factors is complicated by the fact that environmental situations differ from country to country and that there are genetic differences between races.

From the available studies of epidemiology and heritability of allergic diseases, it is clear that allergic diseases are complex, and the interaction between genetics and environmental factors may plays a fundamental role in the development of IgE-mediated hypersensitivity and the subsequent development of clinical symptoms. Epigenetics is a highly sophisticated biological system that regulates the utilization of genomic information by posteriorly modifying/regulating genomic DNA diseases such as allergies involve multiple genetic and environmental factors and epigenetics is drawing attention as a regulatory mechanism that connects these 2 factors [2]. Prescott pointed out that allergic diseases are one type of chronic non-communicable diseases (NCDs) and a common feature shared by these diseases is chronic low-grade inflammation. It is a major global challenge in the 21st century [3]. We need to think and study the epidemiological changes of allergic diseases on a global scale.

The prevalence of atopic allergies differs geographically. Asthma prevalence is low in developing countries, high in Western countries such as the UK, New Zealand, Australia, the Republic of Ireland and Canada and low in Asian countries such as China, Indonesia, and Taiwan. The prevalence of peanut a llergies in Asia is extremely low compared to Western countries. In contrast, the prevalence of food allergies is lower in Western counties than in Asia. Considering these data, it is important to gain insight into the risk factors present in each country. We need to consider the importance not only of allergens, but also of indigenous risk factors for allergies in every country. We need to act locally.