Epithelial barriers are a crucial component of the body's defense system, serving as a protective barrier between the internal and external environments. They are composed of epithelial cells that are tightly packed together, forming a barrier that helps to prevent the entry of pathogens, toxins, and other harmful substances. These barriers are found in various tissues throughout the body, such as the skin, respiratory tract, gastrointestinal tract, and urinary tract. Research in the field of epithelial barriers focuses on understanding the structure and function of these barriers, as well as the mechanisms by which they regulate the movement of molecules and cells across them. This research is important for understanding how epithelial barriers contribute to health and disease, and for developing strategies to enhance barrier function and prevent diseases related to barrier dysfunction, such as inflammatory bowel disease and asthma. Additionally, research in this area can also provide insights into how pathogens and toxins breach epithelial barriers to cause infections and diseases.