What type of reaction does not require sensitization?

An anaphylactoid reaction is a type of hypersensitivity reaction that resembles an anaphylactic reaction but occurs without prior sensitization to an allergen. In anaphylactic reactions, the immune system has been previously exposed to a specific antigen, leading to sensitization and a rapid immune response upon re-exposure.

Anaphylactoid reactions, however, can occur upon the first exposure to certain substances, such as certain medications or contrast dyes. This means that an individual does not need to have developed antibodies or undergone prior exposure to trigger an anaphylactoid response. The underlying mechanisms can involve direct mast cell degranulation and the release of histamine and other mediators, leading to symptoms similar to those seen in anaphylaxis.

In contrast, anaphylactic and anaphylactic shock reactions are closely tied to prior sensitization and require the immune system to have seen the allergen before for a severe, potentially life-threatening response to occur. Minor reactions are typically less severe and do not encompass the severe and systemic nature of anaphylactoid or anaphylactic responses.