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
