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Anaphylaxis
By Mayo Clinic staffMayo Clinic Health Manager
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Definition
Anaphylaxis is a severe, potentially life-threatening allergic reaction. It can occur within seconds or minutes of exposure to something you're allergic to, such as the venom from a bee sting or a peanut.
The flood of chemicals released by your immune system during anaphylaxis can cause you to go into shock; your blood pressure drops suddenly and your airways narrow, blocking normal breathing. Signs and symptoms of anaphylaxis include a rapid, weak pulse, skin rash, and nausea and vomiting. Common triggers of anaphylaxis include certain foods, some medications, insect venom and latex.
Anaphylaxis requires an immediate trip to the emergency room and an injection of epinephrine. If anaphylaxis isn't treated right away, it can lead to unconsciousness or even death.
Symptoms
An anaphylactic reaction is most likely to occur in susceptible people who've been stung by an insect, eaten something they're allergic to, or taken a medication that they are sensitive to. Even if you've only had a mild allergic reaction in the past, you still may be at risk of anaphylaxis.
Anaphylaxis symptoms usually occur within minutes of exposure to an allergen. In rare cases, anaphylaxis occurs more than half an hour after exposure. Anaphylaxis symptoms include:
- Skin reactions including hives and itching, flushed or pale skin (almost always present with anaphylaxis)
- 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
When to see a doctor
If you or someone you're with has a severe allergic reaction, call 911 or seek emergency medical help. If the person having the attack carries an epinephrine auto-injector (such as an EpiPen, EpiPen Jr or Twinject), give him or her a shot right away. Even if symptoms improve after an emergency epinephrine injection, a visit to the emergency department is still necessary to make sure symptoms don't return.
If you had a severe allergy attack or any signs and symptoms of anaphylaxis in the past, make an appointment to see your doctor. Evaluation, diagnosis and long-term management of anaphylaxis are complicated, so you'll probably need to see a doctor who specializes in allergies and immunology.
Causes
Your immune system produces antibodies that defend against foreign substances. This is good when a foreign substance is harmful (such as a bacterium or virus). But some people's immune systems overreact to substances that shouldn't cause an allergic reaction. When this occurs, your immune system sets off a chemical chain reaction, leading to allergy symptoms. In most people, allergy symptoms are not life-threatening. But some people have a severe allergic reaction that can lead to anaphylaxis.
A number of allergens can trigger anaphylaxis, depending on what you're allergic to.
Common anaphylaxis triggers include:
- Certain medications, especially penicillin
- Foods such as peanuts, tree nuts (walnuts, pecans), fish, shellfish, milk and eggs
- Insect stings from bees, yellow jackets, wasps, hornets and fire ants
Less common causes of anaphylaxis include:
- Latex
- Muscle relaxants used in general anesthesia
- Exercise
Anaphylaxis triggered by exercise varies from person to person. In some people, aerobic activity such as jogging triggers anaphylaxis. In others, less intense physical activity such as yard work can trigger a reaction. Eating certain foods before exercise or exercising when the weather is hot, cold or humid has also been linked to anaphylaxis in some people. Talk with your doctor about any precautions you should take when exercising.
Anaphylaxis symptoms are sometimes caused by aspirin, other nonsteroidal anti-inflammatory drugs — such as ibuprofen (Advil, Motrin, others) and naproxen (Aleve, Midol Extended Relief) — and the intravenous (IV) contrast used in some X-ray imaging tests. Although similar to allergy-induced anaphylaxis, this type of reaction isn't triggered by allergy antibodies.
If you don't know what triggers your allergy attack, your doctor may do tests to try to identify the offending allergen. In some cases, the cause of anaphylaxis is never identified. This is known as idiopathic anaphylaxis.
Risk factors
Anaphylaxis isn't all that common, 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 a serious allergic reaction or an anaphylactic reaction before. Future reactions may be more severe than the first reaction, so if you've had a serious allergic reaction in the past, talk to your doctor.
Complications
An anaphylactic reaction can be life-threatening when a severe anaphylactic attack occurs; it can stop breathing or stop your heartbeat. In this case, you'll need cardiopulmonary resuscitation (CPR) and other emergency treatment right away.
Tests and diagnosis
Your doctor will ask you questions about your allergies or any previous allergic reactions you've had. This evaluation will include questions about:
- Whether any particular foods seem to cause a reaction
- Any medications you take, and if certain medications seem linked to your symptoms
- Whether you've had allergy symptoms when your skin has been exposed to latex
- Whether stings from any particular type of insect seem to cause your symptoms
To help confirm the diagnosis:
- You may be tested for allergies with skin tests or blood tests
- You may also be asked to keep a detailed list of what you eat or to stop eating certain foods for a time
Your doctor will want to rule out other conditions as a possible cause of your symptoms, including:
- Fainting spells
- A condition other than allergies that causes flushing or other skin symptoms
- A blood sugar disorder
- Mastocytosis, an immune system disorder
- Psychological issues such as panic attacks
- Heart or lung problems
Treatments and drugs
During an anaphylactic attack, an emergency medical team may perform cardiopulmonary resuscitation (CPR) if you stop breathing or your heart stops beating. You may be given medications including:
- Epinephrine (adrenaline) to reduce your body's allergic response
- Oxygen, to help compensate for restricted breathing
- Intravenous (IV) antihistamines and cortisone to reduce inflammation of your air passages and improve breathing
- A beta agonist (such as albuterol) to relieve breathing symptoms
- Steroid medications to treat or prevent prolonged anaphylaxis symptoms
What to do in an emergency
If you're with someone who is having an allergic reaction and shows signs of shock caused by anaphylaxis, a quick reaction is essential. Signs and symptoms of shock caused by anaphylaxis include pale, cool and clammy skin, weak and rapid pulse, trouble breathing, confusion and loss of consciousness. Even if you're not positive symptoms are caused by anaphylaxis, take the following steps immediately:
- Call 911 or emergency medical help.
- Check the person's pulse and breathing and, if necessary, administer CPR or other first aid measures.
- If the person has medications to treat an allergy attack, such as an epinephrine auto-injector or antihistamines, give them right away.
Using an auto-injector
Many people at risk of anaphylaxis carry an auto-injector. This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh. Always be sure to replace epinephrine before its expiration date, or it may not work properly.
Be sure you know how to use the auto-injector. 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 an epinephrine injection or another medication to treat your symptoms.
Long-term treatment
If your anaphylactic reaction is triggered by insect stings, you may be able to get a series of allergy shots (immunotherapy) to reduce your body's allergic response and prevent a severe reaction in the future.
Unfortunately, in most other cases there's no way to treat the underlying immune system condition that can lead to anaphylaxis. But you can take steps to prevent a future attack — and be prepared in the event one does occur.
- You may need to carry self-administered epinephrine. During an anaphylactic attack, you give yourself the drug using an auto-injector (EpiPen, EpiPen Jr or Twinject).
- Your doctor may recommend taking prednisone or antihistamines.
Prevention
The best way to prevent anaphylaxis is to avoid substances that you know cause this severe reaction. Follow these steps:
- 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 auto-injector. Make sure your auto-injector 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, carefully 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.
Be prepared
It's important to do everything you can to prevent an anaphylactic reaction by avoiding your triggers. But even if you're careful, at some point you'll likely be exposed to the substance you're allergic to. Fortunately, you can be prepared to respond quickly and effectively to an allergy emergency by knowing the signs and symptoms of an anaphylactic reaction. Work with your doctor to develop an emergency plan that specifies what you should do in the event of an anaphylactic attack.
