The epithelial barrier theory suggests that the recent rise in chronic non-communicable diseases, including autoimmune and allergic disorders, is linked to environmental agents that disrupt the epithelial barrier. Over the past six decades, uncontrolled growth, modernization, and industrialization have increased global pollution and exposure to harmful chemicals, leading to documented adverse effects, particularly on the skin and mucosal epithelial barriers. Substances such as particulate matter, detergents, surfactants, food emulsifiers, micro- and nano-plastics, diesel exhaust, cigarette smoke, and ozone have been shown to compromise the integrity of the epithelial barrier. This disruption is associated with the opening of tight-junction barriers, inflammation, cell death, oxidative stress, and metabolic regulation. The interplay of toxic substances, underlying inflammatory diseases, and medications, especially in affected tissues, is a crucial factor to consider. The epithelial barrier is essential for maintaining the structural and functional integrity of the organism. It protects against harmful environmental factors and maintains a beneficial relationship with the microbiota. The integrity of the mucosal barrier relies on intercellular junctions that connect epithelial cells. Tight junctions, adherens junctions, and desmosomes work together to seal off the space between cells, preventing the movement of soluble substances, proteins, and pathogens between the apical and basolateral surfaces. Air pollution, including particulate matter, ozone, nitrogen oxides, and diesel exhaust, contributes to respiratory diseases and has been linked to increased mortality. Indoor pollution is also a significant issue, with pollutant levels often higher indoors than outdoors. Micro- and nano-plastics, due to their widespread use and non-biodegradability, pose a serious threat to nature. These particles can enter the environment and affect various ecosystems, potentially posing risks to human health. Detergents, surfactants, and cleaning agents can damage the skin and mucosal epithelial barriers. Laundry detergents and dishwashers have been shown to induce inflammation and damage to epithelial barriers. Food additives in processed foods can disrupt the epithelial barrier and damage the microbiome, leading to immune system activation. Environmental factors such as air pollution, micro- and nano-plastics, and detergents can cause epithelial barrier damage, leading to dysbiosis, translocation of microbiota, and chronic inflammation. This disruption can result in various diseases, including asthma, atopic dermatitis, and inflammatory bowel disease. The mechanisms of epithelial barrier damage involve direct cell death, metabolic and proinflammatory effects, and oxidative stress. Type 1 and type 2 immune responses contribute to the leakiness of the epithelial barrier, leading to inflammation and disease. Diseases associated with epithelial barrier impairment include asthma, atopic dermatitis, chronic rhinosinusitis, allergic rhinitis, eosinophilic esophagitis, inflammatory bowel disease, and autoimmune disorders. These diseases are linked toThe epithelial barrier theory suggests that the recent rise in chronic non-communicable diseases, including autoimmune and allergic disorders, is linked to environmental agents that disrupt the epithelial barrier. Over the past six decades, uncontrolled growth, modernization, and industrialization have increased global pollution and exposure to harmful chemicals, leading to documented adverse effects, particularly on the skin and mucosal epithelial barriers. Substances such as particulate matter, detergents, surfactants, food emulsifiers, micro- and nano-plastics, diesel exhaust, cigarette smoke, and ozone have been shown to compromise the integrity of the epithelial barrier. This disruption is associated with the opening of tight-junction barriers, inflammation, cell death, oxidative stress, and metabolic regulation. The interplay of toxic substances, underlying inflammatory diseases, and medications, especially in affected tissues, is a crucial factor to consider. The epithelial barrier is essential for maintaining the structural and functional integrity of the organism. It protects against harmful environmental factors and maintains a beneficial relationship with the microbiota. The integrity of the mucosal barrier relies on intercellular junctions that connect epithelial cells. Tight junctions, adherens junctions, and desmosomes work together to seal off the space between cells, preventing the movement of soluble substances, proteins, and pathogens between the apical and basolateral surfaces. Air pollution, including particulate matter, ozone, nitrogen oxides, and diesel exhaust, contributes to respiratory diseases and has been linked to increased mortality. Indoor pollution is also a significant issue, with pollutant levels often higher indoors than outdoors. Micro- and nano-plastics, due to their widespread use and non-biodegradability, pose a serious threat to nature. These particles can enter the environment and affect various ecosystems, potentially posing risks to human health. Detergents, surfactants, and cleaning agents can damage the skin and mucosal epithelial barriers. Laundry detergents and dishwashers have been shown to induce inflammation and damage to epithelial barriers. Food additives in processed foods can disrupt the epithelial barrier and damage the microbiome, leading to immune system activation. Environmental factors such as air pollution, micro- and nano-plastics, and detergents can cause epithelial barrier damage, leading to dysbiosis, translocation of microbiota, and chronic inflammation. This disruption can result in various diseases, including asthma, atopic dermatitis, and inflammatory bowel disease. The mechanisms of epithelial barrier damage involve direct cell death, metabolic and proinflammatory effects, and oxidative stress. Type 1 and type 2 immune responses contribute to the leakiness of the epithelial barrier, leading to inflammation and disease. Diseases associated with epithelial barrier impairment include asthma, atopic dermatitis, chronic rhinosinusitis, allergic rhinitis, eosinophilic esophagitis, inflammatory bowel disease, and autoimmune disorders. These diseases are linked to