Allergic diseases represent a major and growing global health concern, with increasing prevalence among both children and adults. This manuscript presents an extensive review of allergy mechanisms, epidemiology, diagnostics, and clinical challenges, highlighting the complex interplay between immune system dysregulation and environmental exposures. The authors provide a structured analysis of hypersensitivity types, with particular focus on IgE-mediated responses, and emphasize the role of immune barrier defects, epigenetics, and the microbiota in allergic pathogenesis. This manuscript explores diagnostic limitations, including test sensitivity, specificity, and the presence of hidden allergens, as well as challenges in identifying food-related or atypical allergic reactions. A novel and valuable aspect is the discussion of allergy as a potential clinical manifestation of primary immunodeficiencies, such as selective IgA deficiency, Wiskott–Aldrich syndrome, hyper-IgE syndrome, and Netherton syndrome. This review also outlines challenges in treatment, especially among polysensitized patients, and examines the psychosocial burden and complications of allergic diseases, including mental health, nutritional deficiencies, and impaired sleep. This comprehensive synthesis underscores the need for early diagnosis, multidisciplinary management, and personalized therapeutic strategies to improve quality of life of allergic patients.

Oral findings such as inflammation, ulcerations, or lesions can indicate serious systemic diseases and should prompt suspicion of acquired chronic conditions or inborn errors of immunity (IEIs). Currently, there are approximately 500 disease entities classified as IEIs, with the list expanding annually. The awareness of the existence of such conditions is of paramount importance, as patients with these disorders frequently necessitate the utilization of enhanced diagnostic techniques. This is exemplified by patients with impaired antibody production, in whom conventional serological methods may prove to be undiagnostic. Patients with IEI may require distinct therapeutic approaches or antimicrobial prophylaxis throughout their lives. An accurate diagnosis and, more importantly, early identification of patients with immune deficiencies is crucial to ensure the quality and longevity of their lives. It is important to note that the failure to establish a proper diagnosis or to provide adequate treatment could also have legal implications for medical professionals. The article presents IEIs, which may manifest in the oral cavity, and their diagnosis alongside therapeutic procedures.