What is a significant risk factor for hypersensitivity reactions and anaphylaxis?

A significant risk factor for hypersensitivity reactions and anaphylaxis is the administration of a known hypersensitivity reaction (HSR) causing agent. When a patient has a documented allergy or previous hypersensitivity reaction to a specific medication or substance, re-exposure to that allergen can trigger a severe immune response. This is especially true with certain medications, such as antibiotics or chemotherapeutic agents, where the immune system has already been sensitized to the agent, leading to a more intense reaction upon subsequent exposure.

Understanding this risk allows healthcare providers to carefully screen for allergies and previous reactions before administering treatments, ensuring patient safety. In contrast, while low blood pressure, recent surgeries, and high physical activity levels can be associated with various medical conditions or stress responses, they are not direct risk factors for inducing hypersensitivity reactions or anaphylaxis in the same way that exposure to a known allergen is.