Type I hypersensitivity, also known as immediate hypersensitivity or allergic hypersensitivity, is an exaggerated immune response triggered by the release of certain substances in the body upon exposure to a particular allergen. It is considered the most common type of allergic reaction and typically occurs within minutes to hours after exposure.
During a type I hypersensitivity reaction, the allergen stimulates the immune system to produce large amounts of a type of antibody called immunoglobulin E (IgE). These IgE antibodies then bind to specialized cells called mast cells and basophils that are present in various tissues throughout the body, particularly in the respiratory and gastrointestinal tracts, skin, and mucous membranes.
Upon subsequent exposure to the same allergen, the allergen binds to the IgE antibodies attached to the mast cells or basophils, triggering the release of a variety of chemical substances, such as histamine and leukotrienes. These chemical mediators cause inflammation, smooth muscle contraction, mucous secretion, and blood vessel dilation, leading to the characteristic symptoms of type I hypersensitivity including itching, hives, sneezing, wheezing, and in severe cases, anaphylaxis.
Common triggers of type I hypersensitivity reactions include pollen, dust mites, pet dander, certain foods (e.g., peanuts, shellfish), insect stings, and medications. The diagnosis of type I hypersensitivity is typically made through a combination of clinical evaluation, patient history, skin prick testing, and blood tests to measure allergen-specific IgE.
Management of type I hypersensitivity involves allergen avoidance, the use of antihistamines to relieve symptoms, and in severe cases, the administration of epinephrine to immediately reverse the life-threatening effects of anaphylaxis. Long-term management may
