Which of these is NOT a sign of an allergic reaction?

A persistent headache is not typically considered a direct sign of an allergic reaction. Allergic reactions tend to manifest through symptoms that are more directly related to the immune response to an allergen. Common indications of such reactions include wheezing, which reflects respiratory distress due to airway constriction; hypotension, which can occur due to anaphylaxis affecting blood pressure; and burning sensations that may result from inflammation or contact with allergens.

In contrast, a persistent headache can be associated with a variety of non-allergic causes, including tension, migraines, or sinus issues, rather than indicating an immune response. Recognizing the specific signs of allergic reactions is crucial for prompt and appropriate intervention.