How does an anaphylactoid reaction differ from an anaphylactic reaction?

An anaphylactoid reaction differs from an anaphylactic reaction primarily in that it does not require prior sensitization to the antigen. In anaphylaxis, the body's immune system has previously encountered the allergen, leading to the production of specific antibodies (IgE), which trigger an exaggerated response upon re-exposure.

In contrast, an anaphylactoid reaction can occur upon the first exposure to a substance that directly causes mast cell degranulation and the release of mediators such as histamine. This response mimics the symptoms of anaphylaxis, including hives, difficulty breathing, and hypotension, but it occurs independently of previous exposure.

The distinction is significant in clinical practice because it informs how healthcare providers approach treatment and prevention strategies—anaphylaxis typically emphasizes avoiding known allergens, while anaphylactoid reactions can occur unpredictably, necessitating vigilance for potential triggers that have not previously been encountered.