Since the 1960s, more than 350,000 new chemicals have been introduced into the lives of humans and domestic animals. Many of them have become part of modern life and some are affecting nature as pollutants. Yet, our comprehension of their potential health risks for both humans and animals remains partial. The "epithelial barrier theory" suggests that genetic predisposition and exposure to diverse factors damaging the epithelial barriers contribute to the emergence of allergic and autoimmune conditions. Impaired epithelial barriers, microbial dysbiosis, and tissue inflammation have been observed in a high number of mucosal inflammatory, autoimmune and neuropsychiatric diseases, many of which showed increased prevalence in the last decades. Pets, especially cats and dogs, share living spaces with humans and are exposed to household cleaners, personal care products, air pollutants, and microplastics. The utilisation of cosmetic products and food additives for pets is on the rise, unfortunately, accompanied by less rigorous safety regulations than those governing human products. In this review, we explore the implications of disruptions in epithelial barriers on the well-being of companion animals, drawing comparisons with humans, and endeavour to elucidate the spectrum of diseases that afflict them. In addition, future research areas with the interconnectedness of human, animal, and environmental well-being are highlighted in line with the "One Health" concept.

ALL MED Medical Research Institute Wrocław Poland

Department of Biomedical and Diagnostic Sciences Faculty of Medicine University of Salamanca Salamanca Spain

Department of Clinical Immunology Wrocław Medical University Wroclaw Poland

Department of Environmental Health Harvard T H Chan School of Public Health Boston Massachusetts USA

Department of Genetics Faculty of Veterinary Medicine Bursa Uludag University Bursa Türkiye

Department of Otolaryngology Head and Neck Surgery Tongji Hospital Tongji Medical College Huazhong University of Science and Technology Wuhan P R China

Department of Pediatrics Tongji Hospital Tongji Medical College Huazhong University of Science and Technology Wuhan P R China

Division of Food Processing Milk and Dairy Products Technology Program Karacabey Vocational School Bursa Uludag University Bursa Türkiye

Faculty of Medicine Department of Allergy and Clinical Immunology Transylvania University Brasov Romania

Faculty of Science Charles University Prague Czech Republic

Institute of Pathophysiology and Allergy Research Center of Pathophysiology Infectiology and Immunology Medical University of Vienna Vienna Austria

SEED Inc Co Los Angeles California USA

Swiss Institute of Allergy and Asthma Research University of Zurich Davos Switzerland

The Interuniversity Messerli Research Institute of the University of Veterinary Medicine and Medical University Vienna Vienna Austria

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