Abstract:
Background. Allergic reactions are clinical manifestations of hypersensitivity that occur
due to an abnormal immune response to harmless environmental substances such as pollen,
food, or dust. These reactions are common, varying from mild symptoms to severe and lifethreatening conditions requiring urgent medical care.
Objective(s). Classification of allergic reactions by immunologic hypersensitivity types
allows understanding of specific mechanisms and choosing appropriate treatment for each
clinical case.
Materials and methods. For classifying allergic reactions and analyzing the clinical
implications of each immunologic hypersensitivity type, nationally and internationally
recognized guidelines were used, including recommendations from the European Academy of Allergy and Clinical Immunology and the American Academy of Allergy, Asthma, and
Immunology.
Results. Four main types of immunologic hypersensitivity have been identified: Type I,
which is immediate and IgE-mediated, responsible for conditions like anaphylaxis, asthma,
and urticaria; Type II, cytotoxic and mediated by IgG and IgM antibodies, involved in
hemolytic transfusion reactions; Type III, caused by immune complex deposition, commonly
seen in systemic lupus erythematosus and serum sickness; and Type IV, delayed and cellmediated, associated with contact dermatitis and the tuberculin skin test. Each type involves
distinct immunopathological mechanisms crucial for differential diagnosis and personalized
patient treatment.
Conclusion(s). Understanding the types of hypersensitivity enables the comprehension of
complex allergic reactions and contributes to the establishment of an effective therapeutic
plan. Their classification provides an essential framework in internal medicine, clinical
immunology, and allergological practice.
