Name one common sign of an allergic reaction.

Swelling or hives is a classic sign of an allergic reaction. When the body comes into contact with an allergen, it can trigger the immune system to respond, leading to the release of histamines. This chemical response can cause localized swelling, often resulting in hives, which are raised, itchy welts on the skin. Both swelling and hives indicate that the body's immune system is reacting to a perceived threat, which is a hallmark of allergies. Recognizing this sign is crucial for identifying allergic reactions and determining appropriate treatment, such as antihistamines or emergency care in severe cases.

Nausea or vomiting, elevated blood pressure, and shortness of breath can occur in various medical conditions, but they are not the primary or most common indicators of an allergic reaction. Instead, they might indicate other health issues or complications related to allergies, such as anaphylaxis, which requires immediate medical attention. Understanding the primary signs of allergic reactions, like swelling or hives, helps in timely recognition and intervention.