This review examines the relationship between Western lifestyle and the increasing prevalence of allergic and inflammatory diseases. The authors highlight the impact of modernization and industrialization on lifestyles, including changes in diet, exposure to environmental pollutants, and reduced contact with nature. These factors collectively contribute to the disruption of the epithelial barrier, leading to decreased microbiome biodiversity and the development of opportunistic pathogen colonization. The "Epithelial Barrier Theory" integrates previous hypotheses such as the Hygiene Hypothesis, Biodiversity Hypothesis, and Old Friends Hypothesis, emphasizing the role of toxic substances in cleaning agents, detergents, and packaged foods in damaging the epithelial barrier. This disruption triggers a vicious cycle of chronic inflammation, microbial dysbiosis, and epithelial barrier dysfunction, contributing to the development of allergic and other inflammatory diseases. The review underscores the need for further research to understand the molecular mechanisms underlying these diseases and to develop strategies for prevention and treatment.This review examines the relationship between Western lifestyle and the increasing prevalence of allergic and inflammatory diseases. The authors highlight the impact of modernization and industrialization on lifestyles, including changes in diet, exposure to environmental pollutants, and reduced contact with nature. These factors collectively contribute to the disruption of the epithelial barrier, leading to decreased microbiome biodiversity and the development of opportunistic pathogen colonization. The "Epithelial Barrier Theory" integrates previous hypotheses such as the Hygiene Hypothesis, Biodiversity Hypothesis, and Old Friends Hypothesis, emphasizing the role of toxic substances in cleaning agents, detergents, and packaged foods in damaging the epithelial barrier. This disruption triggers a vicious cycle of chronic inflammation, microbial dysbiosis, and epithelial barrier dysfunction, contributing to the development of allergic and other inflammatory diseases. The review underscores the need for further research to understand the molecular mechanisms underlying these diseases and to develop strategies for prevention and treatment.