What Is Anaphylaxis? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Anaphylaxis is a serious allergic reaction that typically affects more than one area of your body at once.

• Immunoglobulin E (IgE) mediated anaphylaxis: An anaphylactic reaction triggered when a particular allergen binds to IgE antibodies on mast cells
• Nonimmune anaphylaxis: An anaphylactic reaction that is not triggered by IgE antibodies — mast cells are directly activated by a trigger

Both types are treated the same way.

In an anaphylactic reaction, your immune system releases a number of chemicals to fight off what it perceives as a dangerous substance invading your body. These immune system chemicals can have different effects in different areas of your body.

An anaphylactic reaction tends to affect multiple areas of your body at once — not just your skin or upper respiratory tract, the way a typical allergic reaction does. Anaphylaxis involves different parts of the immune system, and medical researchers are still working to understand why it may affect areas such as your skin, lungs, digestive tract, or even your heart and blood pressure.

• Rash or hives
• Unease or anxiousness (often described as a “feeling of impending doom”)
• Flushed or pale skin
• Swollen throat and hoarse voice
• Swelling of the face and tongue
• Chest tightness
• Nasal congestion
• Nausea or vomiting
• Weak or rapid pulse
• Dizziness
• Heart palpitations
• Loss of consciousness

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In severe cases, anaphylaxis can cause a person to stop breathing or go into shock — an acute condition that leads to a drop in blood pressure to dangerously low levels. Under these circumstances, anaphylaxis can be fatal unless emergency help is immediately available.

Once the symptoms of anaphylaxis start, they tend to progress quickly.

Any substance can cause an allergic reaction that leads to anaphylaxis, but some substances are more likely to trigger anaphylaxis than others.

Foods that are common triggers include the following:

• Peanuts and tree nuts
• Fish and shellfish
• Milk
• Eggs
• Soy
• Wheat

Drugs that are common causes of anaphylaxis include antibiotics, and aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs).

It’s possible for anyone to have an allergic reaction that causes anaphylaxis at any time, assuming they have previously been exposed to the allergen.

How Allergies Can Lead to Anaphylaxis

An allergic reaction happens when your immune system overreacts to a substance it believes to be a threat, otherwise known as an allergen.

In response to an allergen, your immune system releases chemicals that cause allergy symptoms. These symptoms typically occur in one location of your body for a given allergen.

But in some cases, your immune system releases a wide range of chemicals, and in greater quantities than usual, causing reactions in multiple areas of your body. Collectively, these reactions are known as anaphylaxis.

It’s not fully understood why allergic reactions happen with certain substances in some people and not in others. Genetics is likely involved in some of these differences.

Once your body is sensitized to an allergen, an allergic reaction of any magnitude can occur.

Exercise Can Also Cause Anaphylaxis

Other Risk Factors for Anaphylaxis

For reasons that aren’t fully understood, anaphylaxis is most common in children ages 2 to 12 and in adults ages 50 to 69.

• Asthma
• Cardiovascular disease
• Mast cell disorders
• Peanut or tree nut allergy

To figure out if your symptoms are caused by an allergic reaction or anaphylaxis, your doctor may ask you questions about your previous reactions to foods, medications, insect bites or stings, and latex.

• Blood test for tryptase (an enzyme that may be elevated for up to three hours after anaphylaxis)
• Skin or blood tests for specific allergies
  

The primary treatment for anaphylaxis is epinephrine, usually delivered with an auto-injector, which is available by prescription.

• It causes the blood vessels to constrict, reducing swelling and raising blood pressure.
• It relaxes the muscles of the airways, making it easier to breathe.
• It slows or stops the release of some of the chemicals produced in an allergic reaction.

People who are at risk for anaphylaxis should carry an epinephrine auto-injector or nasal spray with them at all times and familiarize themselves with the instructions for using it.

Epinephrine should be injected into the side of the thigh muscle for rapid absorption. It can be injected through clothing, if necessary.

Once a dose of epinephrine has been injected, the person experiencing anaphylaxis should be taken to the nearest emergency department for further treatment.

Emergency Care 

When you receive emergency care for anaphylaxis, your doctor may decide to treat you with a number of different drugs, such as:

• Epinephrine
• Antihistamines and corticosteroids
• Beta-agonists, such as albuterol (Ventolin)

Antihistamines and corticosteroids are given intravenously (by IV) to reduce inflammation in your airways and help you breathe.

Beta-agonists also can help open up your airways and may be given either by IV or in an inhaled form.

When it comes to anaphylaxis, the best treatment is to prevent the reaction in the first place. This means identifying what you’re allergic to and finding ways to avoid those allergens.

• Read all food package labels carefully to look for allergens.
• Avoid buying food from bulk bins, which might be cross-contaminated.
• Communicate your food needs at restaurants.

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• Make sure family members and friends know about your food allergy.

• Know where you’re likely to encounter the insects you’re allergic to.
• Cover up with clothes and shoes when you go outdoors, and avoid wearing bright colors, such as yellows and reds.
• Avoid drinking from open beverage cans or bottles while outside.
• Learn how to respond if you encounter a biting or stinging insect.

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• Let all your healthcare providers, including your dentist, know about your drug allergy.
• Wear or carry a medical ID that lists your drug allergy or allergies.

Without prompt treatment, anaphylaxis can be life-threatening. It’s essential to seek emergency treatment to minimize the risk of death.

If you receive prompt treatment for anaphylaxis — such as an epinephrine injection, followed by emergency medical care — symptoms usually get better, often without any lasting effects.

An anaphylactic reaction can get worse quickly once it starts, to the point where you collapse, stop breathing, lose consciousness, or have seizures within one to two minutes of its onset — although it may take longer to fully worsen. If treatment isn’t given rapidly, such a reaction can be fatal.

Sometimes symptoms of anaphylaxis return several hours after the initial exposure to an allergen, or even later (known as biphasic anaphylaxis). This second reaction in biphasic anaphylaxis tends to be milder than the first one, but in some cases it may be more severe or even fatal.

• Blocked or closed airway
• Cardiac arrest (no heartbeat)
• Respiratory arrest (no breathing)
• Shock (sudden drop in blood pressure)

Depending on how quickly you receive emergency medical attention, it may be possible to be revived if you experience these complications.

There’s some evidence that Black and Hispanic Americans are at higher risk for food allergies that may lead to anaphylaxis than white or Asian Americans, as well as anaphylaxis itself.

One study found that the overall rate of food allergies was 6.5 percent for Asian Americans, 7.0 percent for white Americans, 8.4 percent for Hispanic Americans, and 8.9 percent for Black Americans. Among those with food allergies, the proportion that reported using an epinephrine auto-injector at least once was 20.9 percent for white participants, 22.6 percent for Asian participants, 23.6 percent for Black participants, and 24.6 percent for Hispanic participants.

• Food allergies
• Drug allergies
• Insect venom allergies
• Latex allergy

• Shock (sudden drop in blood pressure)
• Cardiac arrest (no heartbeat)
• Respiratory arrest (no breathing)

The Takeaway

• Anaphylaxis is a severe type of allergic reaction, involving multiple areas of your body, that requires immediate treatment with epinephrine.
• Some common signs of anaphylaxis include a rash or hives, unease or anxiousness, flushed or pale skin, and swelling of the throat, face, or tongue.
• Even after epinephrine is administered, someone experiencing anaphylaxis should get to the nearest emergency room right away for treatment.