What is the condition called when the immune system launches a defense against an allergen, leading to an adverse reaction?

The condition when the immune system responds to an allergen, triggering an adverse reaction, is best described as an allergic reaction. This occurs when the immune system mistakenly identifies a harmless substance, such as pollen or certain foods, as a threat. In response, it produces antibodies and releases various chemicals, including histamines, which can lead to symptoms like itching, swelling, and trouble breathing.

While anaphylaxis is a severe and potentially life-threatening allergic reaction, it is a specific type of allergic reaction rather than a general term. Intolerance typically refers to a non-immune response to food or substances, like lactose intolerance, which does not involve the immune system. Hypersensitivity is a broader term that can include allergic reactions but also encompasses different types of immune responses that are not strictly allergic in nature. Thus, “allergic reaction” is the most precise term for this condition related to the immune response against allergens.