Anaphylaxis symptoms usually occur within minutes of exposure to an allergen. Sometimes, however, anaphylaxis can occur a half-hour or longer after exposure. In rare cases, anaphylaxis may be delayed for hours. Signs and symptoms include:  Skin reactions, including hives and itching and flushed or pale skin Low blood pressure (hypotension) Constriction of the airways and a swollen tongue or throat, which can cause wheezing and trouble breathing A weak and rapid pulse Nausea, vomiting or diarrhea Dizziness or fainting 
anaphylaxis symptoms occur minutes exposure allergen  sometimes  however  anaphylaxis can occur half-hour longer exposure  rare cases  anaphylaxis may delayed hours  signs symptoms include:  skin reactions  including hives itching flushed pale skin low blood pressure (hypotension) constriction airways swollen tongue throat  can cause wheezing trouble breathing weak rapid pulse nausea  vomiting diarrhea dizziness fainting 
anaphylaxis