Allergen

An allergen is any substance that can provoke an allergic reaction in people who are sensitized to it. In susceptible individuals, exposure to an allergen leads to an immune response mediated by allergen-specific IgE antibodies. Upon subsequent exposure, mast cells and basophils release inflammatory mediators such as histamine, causing symptoms ranging from itching and hives to sneezing, nasal congestion, wheezing, or anaphylaxis. Sensitization occurs when the immune system first encounters the allergen and produces specific IgE; symptoms occur on later exposures.

Common allergens include inhalants such as pollen, dust mites, animal dander, and mold; foods such as peanuts, tree nuts, milk, eggs, shellfish, fish, wheat, and sesame; insect venoms; medications such as beta-lactam antibiotics; and latex. Allergens are often proteins or glycoproteins; cross-reactivity can occur when different allergens share similar protein structures.

Allergic reactions can manifest as allergic rhinitis, allergic conjunctivitis, allergic dermatitis, asthma, or anaphylaxis. Diagnosis relies on patient history, and tests such as skin-prick tests or serum-specific IgE testing; oral food challenges may be used to confirm food allergies.

Management focuses on avoidance of known allergens, pharmacotherapy to control symptoms (antihistamines, intranasal or inhaled corticosteroids, leukotriene receptor antagonists), and emergency treatment with epinephrine for anaphylaxis. For some individuals, allergen immunotherapy (subcutaneous or sublingual) can reduce sensitivity over time.