How many sensitizing exposures to an antigen are required to trigger an anaphylactoid reaction?

An anaphylactoid reaction, unlike anaphylaxis, does not require prior sensitization to an antigen through the production of immunoglobulin E (IgE) antibodies. In fact, it can occur upon first exposure to certain substances that trigger the release of mediators from mast cells and basophils. This release leads to symptoms similar to those seen in anaphylaxis, despite the absence of IgE-related sensitization.

The fundamental nature of an anaphylactoid reaction allows for it to happen upon the initial exposure to a triggering substance, meaning that no previous sensitizing exposures are necessary. This characteristic differentiates it from typical anaphylaxis, which usually does require previous sensitization to the allergen. The lack of need for previous exposures is key in understanding why the correct answer is that none are required to trigger an anaphylactoid reaction.