What condition occurs when chemical mediators are released the first time an antigen is introduced without sensitization?

The condition in question is an anaphylactoid reaction, which occurs when the immune system reacts to an antigen without prior sensitization. Unlike anaphylaxis, which typically develops after the body's immune system has already been sensitized to an allergen and requires a second exposure for symptoms to arise, an anaphylactoid reaction can happen during the first exposure to the antigen.

In these reactions, certain chemical mediators, such as histamines, are released in response to the antigen even though the body has not previously established a memory of that specific allergen. This can lead to symptoms similar to anaphylaxis, including difficulty breathing, swelling, and hives, but it is important to recognize that it is not triggered by an immune response that has been sensitized.

Understanding this distinction is vital for emergency medical responders, as it impacts the approach to treatment and the necessary interventions for a patient experiencing these symptoms.