My goal was to bring an understanding of the complex phenomena of epigenetics and its different mechanisms that can be closely monitored by the help of twin studies specifically focusing on monozygotic twins and discordant studies to explore its potential in understanding hypersensitivity reactions leaning on type 1, to understand their relation. I explored how epigenetic mechanisms like DNA methylation, histone modification, miRNA and other regulatory RNAs function which gives an understanding of how these can alter the activation or deactivation of certain genes. I investigated some twin studies and how they can specifically show the certain genes and epigenetic mechanisms for example the DNA methylation pattern could be different between the MZ twins depending on their lifestyle and environmental changes. I also took a closer look at hypersensitivity reactions pertaining to type 1 reactions and how the different environmental stimuli can induce these hypersensitivity reactions.