The difference between reactogenicity and immunogenicity lies in their different definitions and characteristics. 1. Different definitions: reactogenicity refers to the ability of a pathogen to bind to specific antibodies produced by the body, while immunogenicity refers to the ability of a pathogen to induce the body to produce specific antibodies. 2. Different characteristics: The concepts directly related to reactogenicity and immunogenicity are complete antigen and incomplete antigen. Complete antigens are both immunogenic and reactogenic, such as bacteria and viruses. Incomplete antigens are only reactive but not immunogenic, i.e., they do not require foreign antigens to stimulate the body to produce specific antibodies, such as abnormal proteins and microbial metabolites. Reactogenicity and immunogenicity are two similar concepts, easy to confuse, but as long as the essence of the two can be distinguished. When patients are concerned about antigen and parallel antigen detection, they can consult their doctors for specific analysis to avoid confusing concepts and delaying treatment.