What is a hapten?

A hapten is defined as a molecule that is too small to elicit an immune response on its own. However, when a hapten binds to a larger carrier molecule, typically a protein, it can then become immunogenic, meaning it can trigger an immune response. This characteristic distinguishes haptens from larger, fully formed antigens which are capable of generating an immune response independently due to their size and complexity. Understanding the behavior of haptens is crucial in fields like immunology and vaccine development, where small molecules may need to be conjugated to carriers to effectively stimulate an immune response.