A life-threatening allergic reaction, or anaphylaxis, can cause shock, a sudden drop in blood pressure, and trouble breathing. It can occur minutes after exposure to a specific allergy-causing substance (allergen). However, there may be a delayed reaction or it could occur without an apparent trigger.

Signs and Symptoms
• Skin reactions, including hives, itching, and flushed or pale skin
• Swelling of the face, eyes, lips or throat
• Constriction of the airways, leading to wheezing and trouble breathing
• A weak and rapid pulse
• Nausea, vomiting or diarrhea
• Dizziness, fainting or unconsciousness

Some common anaphylaxis triggers include:

• Medications
• Foods such as peanuts, tree nuts, fish and shellfish
• Insect stings from bees, yellow jackets, wasps, hornets and fire ants

• Immediately call for help. Don't wait to see if condition improves. In severe cases, it can lead to death in a half hour.
• Find out if they are carrying an epinephrine autoinjector to treat an allergic attack. If present, inject by pressing against person's thigh.
• If not, an antihistamine can be used. It isn't sufficient, but it can help relieve symptoms. However, it usually works to slow to be of any real help.
• Have the person lie still on his or her back.
• Loosen tight clothing and cover the person with a blanket. Don't give the person anything to drink.
• If there's vomiting or bleeding from the mouth, turn the person on his or her side to prevent choking.
• If there are no signs of breathing, coughing or movement, begin CPR. Do uninterrupted chest presses — about 100 every minute — until help arrives.
• Get emergency treatment even if symptoms start to improve. After anaphylaxis, it's possible for symptoms to recur. Monitoring in a hospital for several hours is usually necessary.