Hypersensitivity refers to an exaggerated immune response to a substance that is typically harmless. This can occur when the immune system mistakenly identifies a non-threatening allergen, such as pollen or pet dander, as a danger, leading to symptoms like sneezing, itching, or swelling. There are different types of hypersensitivity reactions, classified into four main categories: Type I (immediate), Type II (cytotoxic), Type III (immune complex-mediated), and Type IV (delayed). The severity of hypersensitivity reactions can vary widely, from mild discomfort to life-threatening conditions like anaphylaxis. Treatment often involves avoiding known allergens, using medications such as antihistamines or corticosteroids, and in some cases, undergoing immunotherapy to desensitize the immune system. Understanding hypersensitivity is crucial for managing allergies and improving quality of life for affected individuals.