Allergy

An allergy is an exaggerated immune response to substances that are generally harmless to most people, known as allergens. In many allergic reactions, the immune system produces immunoglobulin E (IgE) antibodies to the allergen. On re-exposure, the allergen cross-links IgE on the surface of mast cells and basophils, triggering release of histamine and other mediators. This inflammatory cascade can affect the skin, eyes, nose, lungs, and gastrointestinal tract, and reactions can range from mild to life-threatening. Allergies are a component of several conditions, including allergic rhinitis, conjunctivitis, eczema, asthma, food allergy, drug allergy, and anaphylaxis.

Common allergens include pollen, dust mites, mold, animal dander, foods such as peanuts, tree nuts, milk, eggs, shellfish and soy, insect venom, and certain medicines. Some individuals experience skin reactions from metal or chemical exposure. Allergic diseases often cluster within individuals and families, and many people have multiple sensitivities or an atopic tendency involving the skin, nose, and lungs.

Diagnosis relies on clinical history and targeted testing. Skin prick testing or specific IgE blood tests can identify sensitization, while oral food challenges may be used under medical supervision to confirm food allergies.

Management emphasizes avoidance of known triggers when possible, along with symptom-relieving medications such as antihistamines, nasal corticosteroids, and, for more severe symptoms, leukotriene receptor antagonists. In cases of anaphylaxis, prompt use of an epinephrine auto-injector is essential. Allergen immunotherapy (subcutaneous or sublingual) can reduce sensitivity for certain allergens. Individuals with suspected food allergies should have an emergency plan and carry appropriate medications.

Global prevalence of allergic diseases is high and varies by region and age. Some allergies resolve in childhood, while others persist and require ongoing management, often with coordinated care among healthcare providers.