What is anaphylaxis?

Anaphylaxis¹ is a potentially life-threatening allergic reaction.

Anaphylaxis occurs when you’re exposed to something you're allergic to, such as food, an insect sting, or medication. Rarely, latex exposure and exercise can also cause anaphylaxis in some people.

Anaphylaxis can be prevented by managing risk factors and avoiding specific allergens or triggers. If you are at risk for having anaphylactic attacks, you should remain prepared for one to occur. Knowing the symptoms of an attack and carrying self-injecting epinephrine can help you respond effectively to an allergic reaction.

How common is anaphylaxis?

Anaphylaxis can affect anyone with a serious allergy—even those that are young and healthy. According to an Asthma and Allergy Foundation of America (AAFA) study printed in the Journal of Allergy and Clinical Immunology (JACI), anaphylaxis occurs in about 2% (one in 50)² of Americans. The Journal of Allergy and Clinical Immunology also reports that up to 5%³ of Americans have experienced anaphylactic shock.

Anaphylaxis is rarely fatal. Among people hospitalized for anaphylaxis in the US, between 0.25% and 0.33% were fatal⁴. The inability to breathe and cardiovascular collapse are responsible for most fatalities.

Anaphylaxis causes

Allergic reactions⁵ occur when the immune system overreacts to an allergen, such as pollen, pet dander, or a specific food. Unlike viruses and certain bacteria (which can also cause your body to react protectively), allergens are not directly harmful to the body.

The substances that most commonly trigger anaphylaxis⁶ are foods (particularly milk, soy eggs, nuts, and shellfish), medications, animal venom (such as insect stings), IV contrast dyes, and latex.

During an allergic reaction, the immune system can cause the skin, sinuses, airways, and/or digestive system to become inflamed. A mild allergic reaction can include symptoms like sneezing, itching, coughing, a runny nose, and red or watery eyes. These symptoms can often be easily treated with either over-the-counter (OTC) or prescription medications.

Anaphylaxis is a particularly severe allergic reaction⁷ that can impact the functioning of your lungs and heart. An anaphylactic event requires immediate emergency medical treatment.

Anaphylactic attacks are often sudden. Seconds or minutes after your exposure to a trigger, your immune system releases a flood of chemicals that can launch it into anaphylactic shock. When anaphylactic shock occurs, your blood pressure drops suddenly and your airways narrow, which can make breathing difficult or prevent you from breathing entirely.

During an allergic reaction, your body produces antibodies (known as immunoglobulins) that bind to the foreign materials (antigens), thus provoking the allergic reaction.

Next, this binding between antibodies and antigen triggers an excessive reaction from cells in your tissue that mediate inflammatory responses (mast cells⁸). These mast cells release mediators, like histamine, into the surrounding tissues.

These chemical mediators can⁹ narrow your airways, widen your blood vessels, increase the leakage of fluid from blood vessels, and interrupt the flow of blood to your heart.

The symptoms of anaphylaxis include a weak, rapid pulse, an itchy skin rash, throat or tongue swelling, shortness of breath, as well as nausea and vomiting. Common triggers could be specific foods or medications, insect venom, and latex.

The primary treatment of anaphylaxis is an injection of epinephrine.¹⁰ If you don't have epinephrine with you, you need to go to an emergency room immediately. It’s important that you go to the emergency room for treatment even after using epinephrine. Anaphylaxis can be fatal when it isn’t treated right away.

Anaphylaxis symptoms

The symptoms of anaphylaxis¹¹ are usually felt within minutes of your exposure to an allergen. However, in some cases, the signs of anaphylactic shock can take a half-hour or longer to appear after exposure.

Some common signs and symptoms of anaphylaxis include:

• Skin reactions, including itching, hives, and flushed or pale skin
• Constriction of your airways, which can cause wheezing and trouble breathing
• Nasal congestion, sneezing, hoarseness, cough
• A swollen tongue or throat
• Low blood pressure (hypotension)
• A weak and rapid pulse
• Nausea, vomiting, abdominal pain, or diarrhea
• Dizziness or fainting
• An impending sense of death

Because it can cause your breathing or heartbeat to stop, an anaphylactic reaction can be life-threatening.

Seek emergency medical help immediately if you or someone you’re with has a severe allergic reaction. Do not take any time to wait for the symptoms to go away.

If the person having the anaphylactic attack carries an epinephrine auto-injector¹² (EpiPen or EpiPen Jr.), administer it immediately.

Even if your condition improves after an injection, you’ll still need to go to an emergency room in case symptoms recur.

Rebound or biphasic anaphylaxis

Your body may have a second anaphylactic reaction, even after an initial episode is treated and the symptoms go away. This second reaction, known as biphasic or rebound anaphylaxis, can happen without any additional exposure to the allergen.

The second reaction can range in severity from mild to severe. However, most late-phase reactions are mild to moderate in severity.

It’s unclear what causes this late-phase reaction. Risk factors for a late-phase reaction include a delayed dose of epinephrine or not enough epinephrine given for the first response.

The risk for rebound anaphylaxis is what makes it so important that you go seek emergency medical treatment if you experience a severe allergic reaction. The recurrence rate of anaphylactic shock is as high as 20%¹³, and biphasic responses can occur anywhere between 1–72 hours after the initial episode (most commonly within 8–10 hours).

What is anaphylactic shock?

You may have heard the term “anaphylactic shock” being used to describe an especially dangerous allergic reaction. Anaphylactic shock,¹⁴ like anaphylaxis, is a life-threatening emergency.

Anaphylaxis and anaphylactic shock are terms often referenced interchangeably. Some medical professionals use “anaphylactic shock” to describe the most severe, life-threatening type of allergic reaction.

A person going into anaphylactic shock may have the following symptoms:

• Fast heartbeat
• Feeling uneasy and agitated
• Skin turning blue or white
• Swelling of the lips or face
• A grating, grainy cough
• Wheezing
• Trouble breathing
• Hives, particularly over several areas of the body

During anaphylactic shock, blood pressure drops very low and blood has trouble circulating throughout the body. Some people may also lose bladder or bowel function, experience chest pain, or become unconscious.

Anaphylactic shock can be hard to distinguish from other causes of shock. Still, the condition can be easily detected in most people because of recent exposure to an allergen.

Anaphylactic shock can lead to life-threatening complications.¹⁵ It can block your airways and stop your breathing. Not being able to breathe for an extended period can lead to brain damage.

Anaphylactic shock can also affect the heart, stopping it from pumping enough blood to your body (cardiogenic shock), cause an abnormally fast or slow heartbeat (arrhythmia), or trigger a heart attack. Its effects on your blood vessels can also lead to kidney failure.¹⁶

Anaphylactic shock treatment

Treatments for anaphylactic shock¹⁷ are the same as treatments for anaphylaxis.

The primary treatment for people experiencing anaphylactic shock is an injection of epinephrine (EpiPen or EpiPen Jr.). Epinephrine works by reversing the action of anaphylaxis.

You should still see a medical provider even if you feel better after using the EpiPen, since the reaction may return after the medication wears off.

If an insect sting has caused the anaphylactic shock, remove the stinger if possible. Use a thin object, such as a plastic card, to dislodge the stinger. Make sure not to squeeze the stinger, since this may cause it to release more venom.

Call 911 if you see someone going into anaphylactic shock. Then, do the following:

• If they have an EpiPen (or EpiPen Jr for children), administer it immediately.
• Put the person into a comfortable position. Elevating their legs can keep their blood moving towards vital organs.
• If the person isn’t breathing, administer CPR.

People who are at risk for anaphylaxis or who have had anaphylactic reactions in the past should carry an epinephrine injector at all times.

Anaphylaxis triggers

There are certain tests that can help you identify your specific allergens.

The most common anaphylaxis triggers include:

• Food allergies, such as allergies to eggs, peanuts, tree nuts, fish, shellfish, and milk
• Certain medications, such as antibiotics, aspirin, penicillin, and other over-the-counter (OTC) pain relievers
• Insect stings from bees, yellow jackets, hornets, wasps, and stinging ants
• Latex¹⁸—specifically, natural rubber latex found in medical supplies (disposable gloves, dental dams, stethoscopes, bandages) and consumer products (balloons, condoms, tires)

Anaphylaxis risk factors

Not many risk factors for anaphylaxis¹⁹ are known today. Some factors that may increase your risk of having an anaphylactic episode include previous cases of anaphylaxis, allergies or asthma, and having a condition like heart disease.

Known anaphylaxis risk factors²⁰ can vary according to their cause. For instance, past or present cardiovascular problems and being of an older age can put you at higher risk for fatal drug anaphylaxis.

Fatal food anaphylaxis is most common in people in their 20s and 30s. One significant risk factor for this type of reaction is the delayed administration of epinephrine.

Is it always an allergic reaction?

While an allergic reaction is the most common cause of anaphylaxis, there are cases in which anaphylaxis is not caused by an allergic reaction. Some people may develop anaphylaxis from exercise.

In rare instances, anaphylaxis has been linked to eating certain foods before exercise or exercising when the weather is humid, hot, or cold and humid. Talk with your provider if you suspect that exercise may have caused an allergic reaction.

What causes food allergies?

The existence of allergic hypersensitivity to food²¹ has been reported since the oldest known civilizations. Still, our knowledge about the causes of food allergies is limited.

Food allergies affect approximately 4% of adults and 8% of children²². Scientists suspect that certain genes, as well as conditions in the stomach and gut, may contribute to food allergies. There is no cure for food allergies—avoiding trigger food(s) is the only way to prevent an allergic reaction.

In the United States, the most serious allergic reactions are caused by eight food groups: milk, eggs, fish, crustacean shellfish, wheat, soy, peanuts, and tree nuts.

Oral allergy syndrome (OAS)²³ is a common form of food allergy. You may have OAS if your throat or mouth itches after eating certain vegetables or fruits. After consuming an allergen, itching and swelling may be felt in the lips, tongue, or throat. Allergic reactions caused by OAS are not likely to turn into anaphylaxis.

An allergist or immunologist can help you determine what foods you are allergic to. They can administer a skin prick test, which involves exposing your skin to small amounts of different allergens.

The specialist will monitor your reaction to each substance, helping them to determine what you may be allergic to. You will know which allergens you react to if they cause an itchy, dime-sized spot to appear after a few minutes.

When a reaction to a particular substance is severe, a medically supervised food challenge²⁴ may be necessary to confirm the results of a skin test. Food challenges are only conducted by experienced clinicians in facilities that can treat life-threatening anaphylaxis.

A food challenge involves eating increasing amounts of particular food suspected of causing your allergies. You will be treated right away if an allergic reaction begins. Allergies are ruled out if you are able to eat a regular serving of the food without presenting with a reaction.