What is a common symptom of anaphylaxis in response to an allergen?

A common symptom of anaphylaxis in response to an allergen is urticaria, which is the medical term for hives. Urticaria typically presents as raised, itchy welts on the skin and can occur rapidly during an anaphylactic reaction. This reaction is part of the body's hyper-responsive immune system, where the release of histamines and other chemicals leads to inflammation and swelling in various tissues, including the skin.

Urticaria is particularly notable in anaphylaxis because it can serve as a visible indicator of the body's systemic response to an allergen. Other symptoms of anaphylaxis may include difficulty breathing, swelling of the throat, rapid heartbeat, and gastrointestinal issues, but urticaria specifically highlights the skin's reaction during such acute allergic responses.