RELATED STORIES • Anaphylaxis: First aid • Exercise-induced anaphylaxis

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Anaphylaxis is a severe and potentially life-threatening allergic reaction. Common triggers of anaphylaxis include foods, certain medications, insect venoms and latex.

Your immune system produces antibodies that defend against foreign substances, including allergens. When antibodies attach to these foreign substances, they may release chemicals that can cause allergy signs and symptoms such as watery eyes and a runny nose. Anaphylaxis occurs when your immune system severely reacts to an allergen. The flood of chemicals released in your body during anaphylaxis makes your blood pressure drop suddenly and your bronchial tubes narrow, causing difficulty breathing or even unconsciousness and death. You may have an anaphylactic response within seconds or minutes of exposure to an allergen such as the venom from a bee sting or an ingested peanut.

Although anaphylaxis is the most dangerous type of allergic reaction, it's also the least common. Fortunately, you can be prepared to respond quickly and effectively to an allergy emergency by knowing the signs and symptoms of a severe allergic reaction and by carrying emergency medication with you. It's also important to do everything you can to prevent exposure to life-threatening allergens.

An anaphylactic reaction is most likely to occur in susceptible people who've been stung by a bee, eaten food containing food allergens, or taken a medication that they are sensitive to. The effects of anaphylaxis aren't limited to the site of the exposure. Development of the following signs and symptoms within minutes of exposure to an allergen is a strong indication of anaphylaxis:

• Constriction of the airways, including wheezing and a swollen tongue or throat, that results in difficulty breathing
• Shock associated with a severe decrease in blood pressure
• Weak and rapid pulse
• Dizziness or fainting
• Hives and itching
• Flushed or pale skin
• Nausea, vomiting or diarrhea

Many allergens can cause anaphylaxis. Sometimes the cause of an anaphylactic reaction is unknown. The most common causes of anaphylaxis include:

• Drugs, such as penicillin
• Foods such as peanuts, tree nuts (walnuts, pecans), milk, eggs, fish and shellfish
• Insect stings from bees, yellow jackets, wasps, hornets and fire ants
• Latex

Anaphylaxis isn't a common condition, though many people are at risk of having an anaphylactic reaction. If you have a history of allergies or asthma, you may be at increased risk — especially if you've had an anaphylactic reaction before. Future reactions may be more severe than the first.

See a specialist in allergies and immunology if you have experienced an episode of anaphylaxis or think you've experienced some of the signs and symptoms associated with it. An evaluation typically includes questions about:

• Food
• Medications
• Latex
• Insect stings

You may be tested for allergies with skin tests or blood tests. The specialist can provide you instructions on how you might prevent future anaphylactic reactions and how to self-administer medication if you do have a reaction. You may also be asked to keep a detailed list of what you eat or to stop eating certain foods for a time.

Adrenaline (epinephrine) is the drug most commonly used to treat anaphylactic reactions. You can self-administer the drug with an auto-injector, such as the EpiPen, EpiPen Jr or Twinject. An auto-injector is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh. Your doctor may recommend that you carry an epinephrine auto-injector with you. Be sure you know how to use the auto-injector properly. Also, make sure the people closest to you know how to administer the drug — if they're with you in an anaphylactic emergency, they could save your life. Medical personnel called in to respond to a severe anaphylactic reaction also may give you epinephrine.

If necessary, a doctor or emergency medical team may perform cardiopulmonary resuscitation (CPR). They may also administer intravenous antihistamines and cortisone to reduce inflammation of your air passages and improve your breathing.

If you're with someone who has experienced anaphylaxis and shows signs of shock — pale, cool and clammy skin, weak and rapid pulse, shallow breathing, confusion, anxiety — follow these steps:

• Call 911 or emergency medical help immediately.
• Check to see if the person is carrying special medications to treat an allergy attack. If so, administer the medication.
• Get the person to lie down on his or her back. Elevate the feet higher than the head to keep adequate blood flow to the brain, which will prevent fainting. Keep him or her from moving unnecessarily.
• Keep the person warm and comfortable. Loosen tight clothing and cover him or her with a blanket. Don't give the person anything to drink.
• If the person is vomiting or bleeding from the mouth, place the person on his or her side to prevent choking.

If the person isn't breathing or has no pulse, perform CPR.

The best way to prevent anaphylaxis is to avoid substances that you know cause this severe reaction. Follow these steps to help ensure your well-being:

• Wear a medical alert necklace or bracelet to indicate if you have an allergy to specific drugs or other substances.
• Alert your doctor to your drug allergies before having any medical treatment. If you receive allergy shots, always wait at least 30 minutes before leaving the clinic so that you can receive immediate treatment if you have a severe reaction to the allergy shot.
• Keep a properly stocked emergency kit with prescribed medications available at all times. Your doctor can advise you on the appropriate contents. This may include an epinephrine autoinjector. Make sure your autoinjector has not expired. These medications generally last 18 months.
• If you're allergic to stinging insects, exercise caution when they're nearby. Wear long-sleeved shirts and trousers. Avoid bright colors and don't wear perfumes or colognes. Stay calm if you come in proximity to a stinging insect. Move away slowly and avoid slapping at the insect.
• Avoid wearing sandals or walking barefoot in the grass if you're allergic to insect stings.
• If you have specific food allergies, read the labels of all the foods you buy. Manufacturing processes can change, so it's important to periodically recheck the labels of foods you commonly eat. When eating out, ask about ingredients in the food, and ask about food preparation because even small amounts of the food you're allergic to can cause a serious reaction.