How long does a breakout from a allergic reaction take to heal?

Depends on severity. Minor allegic reactions, with local swelling and itching, usually resolve within 30 to 60 minutes. When someone has a more severe reaction, in which swelling or hives occur, sometimes the reactions take several days to resolve. As always, if you are ever having a reaction in which breathing is compromised or there is swelling in the throat, call 911 immediately.