Allergic

Allergic describes anything related to allergies, or a person who experiences hypersensitivity to typically harmless substances such as pollen, foods, animal dander, or medications. Allergic reactions result from an overactive immune response that can range from mild to life-threatening.

Most allergic reactions are mediated by immunoglobulin E (IgE) antibodies. Upon first exposure, the immune system becomes sensitized to the allergen. On subsequent exposures, cross-linking of IgE on mast cells and basophils triggers release of histamine and other mediators, causing symptoms. Not all reactions are IgE-mediated; some involve other immune pathways and present differently.

Common allergic disorders include allergic rhinitis (nasal congestion, sneezing, itchy eyes), allergic conjunctivitis, asthma with reversible airway obstruction, atopic dermatitis (eczema), food allergies, and contact dermatitis. Severe reactions can lead to anaphylaxis, a rapid, systemic response requiring emergency treatment.

Diagnosis depends on clinical history and testing. Skin prick or intradermal testing assesses sensitization, while serum-specific IgE tests measure circulating antibodies. In foods, oral food challenges under medical supervision are sometimes used. Management focuses on avoidance of known allergens, pharmacotherapy to control symptoms, and emergency preparedness for anaphylaxis.

Treatment may include antihistamines, intranasal or inhaled corticosteroids, leukotriene antagonists, and bronchodilators. Epinephrine auto-injectors are critical for anaphylaxis. Allergen immunotherapy (shots or sublingual tablets) can modify the immune response for some allergens. Biologic therapies targeting IgE or other immune pathways are used for certain conditions, such as severe asthma or chronic urticaria.

Prevention and public health strategies emphasize accurate labeling of products, education on avoidance, and prompt recognition of severe reactions. The term allergic is distinct from intolerance, which generally does not involve the immune system, and from non-allergic hypersensitivity.