What is a common symptom indicating an allergic reaction?

A common symptom indicating an allergic reaction is flushed skin. This reaction can occur when the body's immune system identifies a normally harmless substance, such as pollen, food, or medications, as a threat. The immune system then releases chemicals like histamines, which can cause various symptoms, including redness and warmth of the skin, often leading to flushing. This is a typical physiological response as blood vessels dilate in an effort to increase blood flow and promote healing or response to the perceived allergen.

While fever, headache, and dizziness are symptoms that can arise from a variety of conditions, including infections or other illnesses, they are not specific indicators of an allergic reaction. In contrast, flushed skin is more directly associated with the body's immediate response to allergens.