Which of the following is a symptom of an allergic reaction?

Hives, also known as urticaria, are a classic symptom of an allergic reaction and occur when the body's immune system reacts to an allergen. This response triggers the release of histamines and other chemicals, leading to localized swelling, redness, and itching on the skin. Hives can appear as raised welts and may vary in size, often presenting suddenly in response to allergens such as food, medications, or environmental triggers.

While headaches, nausea, and sore throats can be associated with various conditions and may occur during allergic reactions in some instances, they are not specific symptoms of an allergic response. Headaches might result from tension or other health issues, nausea can stem from gastrointestinal problems, and a sore throat might indicate an infection or irritation unrelated to an allergy. Hives remain the most significant and direct indicator of an allergic reaction, highlighting the body's hypersensitivity to specific substances.