What is a key characteristic of a hypersensitivity reaction (HSR)?

A key characteristic of a hypersensitivity reaction is localized tissue injury. Hypersensitivity reactions are categorized into four types, with each type exhibiting different mechanisms and effects on the body. Localized tissue injury typically occurs in response to an allergen or immune trigger, leading to symptoms in specific areas of the body, such as skin, respiratory system, or gastrointestinal tract.

In many cases, the injury results from the immune system's overreaction, causing inflammation and damage to tissues in the area affected. Examples include allergic reactions like contact dermatitis or asthma, where the localized response can lead to swelling, redness, and other symptoms.

While systemic and severe reactions, immediate respiratory distress, and the release of cortisol can be associated with certain hypersensitivity responses, they are not universally characteristic of all types of hypersensitivity reactions. For instance, systemic reactions often pertain to anaphylaxis, which is a specific severe type of hypersensitivity. Immediate respiratory distress might be seen in certain asthma attacks or anaphylactic reactions but is not a defining feature of all hypersensitivity types. Similarly, cortisol release could occur in response to stress or inflammation but isn't a unique aspect of hypersensitivity reactions themselves.