What is the primary characteristic of anaphylaxis?

The primary characteristic of anaphylaxis is its rapid onset, typically occurring within 15-20 minutes following exposure to an allergen. This time frame is crucial because it highlights the urgency of recognizing anaphylactic reactions, which can progress quickly from mild symptoms to more severe complications, including respiratory distress and shock.

In contrast, the other options refer to aspects of allergic reactions that do not apply to anaphylaxis. For example, delayed reactions are usually associated with different types of hypersensitivity responses, which can occur hours or days after exposure. Anaphylaxis is not considered a minor allergic reaction; rather, it is a severe and life-threatening condition that requires immediate medical attention. Additionally, while anaphylaxis can significantly affect the respiratory system, it may also involve other systems, including the cardiovascular and gastrointestinal systems, making it much broader than just respiratory symptoms.