Which symptom is indicative of an allergic reaction?

The symptom that indicates an allergic reaction is pale skin. When the body experiences an allergic reaction, it can trigger histamine release, which leads to various physiological changes. In certain cases, such as anaphylaxis, blood vessels may dilate, causing blood pressure to drop and potentially leading to pale or cool skin. This sign is often associated with severe allergic reactions, where the body is reacting aggressively to an allergen.

Other symptoms typically associated with allergic reactions might include hives, swelling, or difficulty breathing, but pale skin specifically points to a more severe systemic response that should be treated urgently.

To clarify the other symptoms: a severe headache is more commonly associated with migraine or tension-type headaches. Fever is indicative of an infection or illness rather than an allergic response. Similarly, stomach cramps can result from various conditions, including gastrointestinal issues, but are not specifically indicative of an allergy.