Allergic diseases are a major health problem especially in rapidly developing and high-income societies. They require chronic treatment and have a significant impact on quality of life (QoL) of the individuals, families and communities affected by them; in addition, they are a burden on limited health resources. What really causes allergic disease and why do some human beings develop them, whereas others do not? There are multiple layers to this immunological enigma that have been partially unraveled over the past few years. The development of atopy – or a genetic predisposition to allergic diseases and asthma – has been examined and, undoubtedly, allergic inflammation in an individual is a delicate interplay between their genetic milieu (which includes conventional chromosomal DNA and epigenetic DNA) and the environment.