How fast can hives spread?

Very rapidlly: Some allergic reactions are more aggressive than others and spread rapidly. In this case the patient needs emergency medical evaluation.

Within minutes: People can develop head to toe hives within minutes of, for example, eating a food to which they are allergic. Hives are not contagious so do not spread from person to person. Individual hives only last from 1-24 hours but new crops can replace them. Consult an allergist to help determine cause and best treatment.