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.

It can be triggered by exposure to any allergen — a substance that you’ve become allergic to. The most common triggers are foods, medications, insect venom, and latex.

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 on different areas of your body.

If it’s severe enough and left untreated, anaphylaxis can cause you to go into shock. Signs of shock often include rapid breathing, pale or clammy skin, dizziness, and a rapid, weak pulse.

Anaphylaxis requires immediate treatment with an epinephrine injection — this usually is administered before the person gets to a hospital emergency room, where they should go as soon as possible.

If you know that you’re prone to an anaphylactic reaction, you should carry an epinephrine self-injection device with you at all times. You should also do everything in your power to avoid known triggers of anaphylaxis.

Because anaphylaxis involves so many different parts of the immune system, medical researchers are still working to understand why it may affect anything from your skin, lungs, GI tract, or even your heart and blood pressure.

Anaphylaxis has become more common in recent years, especially in children and younger adults, for reasons that aren’t fully understood. (1,2,3,4)

What Happens in Anaphylaxis

Anaphylaxis refers to a number of allergic reactions happening in your body at almost the same time. It’s set off by numerous chemicals released by your immune system in various tissues throughout your body.

These chemical groups include arachidonic acid metabolites, chemokines, cytokines, proteases, and proteoglycans. Each of these groups contains more specific chemicals.

One chemical implicated in anaphylaxis is histamine, which is the target of antihistamine drugs. Histamine is one player in the process that relaxes your blood vessels, tightens your throat and airways, and increases mucus production.

But because histamine is only one of numerous chemicals involved in an anaphylactic reaction, taking an antihistamine by itself tends to have limited benefits.

Each chemical released in an anaphylactic reaction is responsible for a specific task, and some are more associated with certain symptoms than others. (4)

How Allergies Lead to Anaphylaxis

An allergic reaction happens when your immune system overreacts to a substance it believes to be a threat, 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. (5)

Allergies happen when your immune system becomes sensitized to a particular substance. It’s not fully understood why this happens with certain substances in some people and not in other people. 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. (1)

Anaphylactic and Anaphylactoid Reactions

Sometimes, a substance can set off a reaction that’s similar to anaphylaxis the very first time you’re exposed to it. This isn’t a true allergic reaction, since your body hasn’t become sensitized to the substance.

Called an anaphylactoid reaction, this can happen in response to drugs like morphine (OMS) and aspirin (Vazalore), as well as contrast medium (a substance that’s introduced into the body for certain imaging tests). It can also be caused by exercise.

Even though the chemicals released in your body may be somewhat different in an anaphylactoid reaction compared with a true anaphylactic one, the symptoms, treatment, and risk of complications are the same for both. (1,3)

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.

Symptoms of anaphylaxis may include the following:

• 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 (1,2)

In severe cases, anaphylaxis can cause a person to stop breathing or to 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. (2)

Anaphylaxis symptoms usually begin within 15 minutes after you come into contact with the allergen that causes it, although in some cases it can take an hour or more for anaphylaxis to develop. (3)

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

Recognizing the signs and symptoms of anaphylaxis — and knowing how to treat it — is crucial to preserve life. (1)

Learn More About the Signs and Symptoms of Anaphylaxis

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 of anaphylaxis include the following:

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

Drugs that are common causes of anaphylaxis include antibiotics, aspirin, blood and blood products, certain hormones, and opioids.

Bites or stings from fire ants, bees, wasps, and hornets are more likely than other types of insect bites or stings to cause anaphylaxis.

Certain substances and activities can also trigger what’s known as an anaphylactoid reaction. The reaction isn’t allergic in the sense of your body being sensitized to an allergen, but the effects and treatment are virtually the same. Common triggers of an anaphylactoid reaction include contrast medium, aspirin and other NSAIDs, opioids, monoclonal antibodies, exercise, and certain antibiotics, such as quinolones and vancomycin (Firvanq).

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

But certain groups are more likely to have anaphylaxis in response to particular allergens.

For example, children are more likely than adults to experience anaphylaxis in response to a food allergy. Adults are more likely to experience it because of an allergy to antibiotics, anesthetics, contrast medium, or insect venom.

Men are more likely than women to experience anaphylaxis from insect venom, while women are more likely to experience it from latex, aspirin, contrast medium, and muscle relaxants.

For reasons that aren’t completely clear, people with a higher socioeconomic status — those with a higher income, education, and other measures of social status — are at greater risk for anaphylaxis.

Also for reasons that aren’t fully understood, prescription rates for self-injectable epinephrine — which is prescribed to treat anaphylaxis — are higher in northern than in southern areas of the United States.

You’re more likely to experience anaphylaxis if you have certain other medical conditions, including:

• Asthma
• Cardiovascular disease
• Mastocytosis (abnormal accumulation of mast cells in the skin, bone marrow, and internal organs)
• Substance use disorders

You’re at greater risk for anaphylaxis if you’re genetically predisposed to allergic diseases — a condition known as atopy. But this increased risk may not apply to certain allergens, such as penicillin, insulin, or some insect venoms.

Generally speaking, your risk for anaphylaxis goes down the longer you go without being exposed to an allergen that may cause it. (4)

Learn More About Causes of Anaphylaxis: Common Risk Factors, Genetics, and More

Surprising Triggers for Anaphylaxis

Most people have heard that peanuts can cause anaphylaxis if you’re allergic to them, but did you know that some women experience anaphylaxis during a certain phase of their menstrual cycle? Or that a bite from a lone star tick can lead to an allergy to red meat?

Many seemingly weird things can bring on anaphylaxis in people who are susceptible to it, and in some cases it can be difficult to figure out what’s causing it.

If you’re experiencing symptoms of anaphylaxis but aren’t sure what’s causing it, see an allergist for help.

Learn More About Surprising Triggers for Anaphylaxis

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.

To help confirm a diagnosis of anaphylaxis, your doctor may order the following tests:

• Blood test for tryptase (an enzyme that may be elevated for up to three hours after anaphylaxis)
• Skin or blood tests for specific allergies (2)

Your doctor may also ask you questions, and possibly order tests, to rule out health conditions that may have symptoms similar to those of anaphylaxis. (4)

Prognosis of Anaphylaxis

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. (1)

Symptoms of anaphylaxis often develop within a few seconds or minutes after exposure to an allergen, but can take an hour or longer to develop in rare cases. (1,3)

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 4 to 8 hours after the initial exposure to an allergen, or even later (known as biphasic anaphylaxis). This second reaction tends to be milder than the first one, but in some cases it may be more severe or even fatal. (3,6)

Some people have what’s known as protracted anaphylaxis, in which symptoms last for several hours or longer. This possibility is one reason it’s important to be monitored in an emergency medical setting, even if your symptoms are initially resolved by an epinephrine injection. (6)

The primary treatment for anaphylaxis is epinephrine, usually delivered with an auto-injector, which is available by prescription. Epinephrine reverses the symptoms of anaphylaxis in several ways:

• 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. (2,7)

People who are at risk for anaphylaxis should carry an epinephrine auto-injector 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.

Sometimes a second dose of epinephrine is needed, if anaphylaxis symptoms recur. If this is necessary, a new auto-injector should be used. (7)

Once a dose of epinephrine has been injected, the person experiencing anaphylaxis should be taken to the nearest emergency department for further treatment. (6)

To help prevent shock (a sudden drop in blood pressure) during an anaphylactic reaction, after receiving epinephrine, the person should lie flat on their back with their feet elevated about 12 inches (30 centimeters) and covered by a coat or blanket. This should only be done if it feels comfortable for the person and if no injuries are suspected. (1)

If you stop breathing or your heart stops beating due to anaphylaxis, medical personnel may perform cardiopulmonary resuscitation (CPR). (2)

Medication Options

Epinephrine is the first-line treatment for anaphylaxis and should always be given as soon as possible after the onset of symptoms. (6)

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

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

Antihistamines and corticosteroids are given intravenously (by IV) to reduce inflammation of 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.

You may also be given fluids by IV to increase your blood volume and blood pressure, or given oxygen through a tube to help you breathe. (2,3)

Learn More About Treatment for Anaphylaxis: Medication, Surgery, and More

Prevention of Anaphylaxis

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.

For people with food allergies, that means being sure to:

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

For people with insect venom allergies, you should:

• 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 brightly colored clothing items, 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.

If you’re allergic to drugs, take these steps:

• 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. (1,2)

Learn More About Preventing Anaphylaxis

If you don’t receive prompt treatment, anaphylaxis can lead to a number of potentially life-threatening complications, including the following:

• 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. (1,2)

Many experts believe that anaphylaxis is underdiagnosed and underreported, so it’s difficult to know how common it is.

It’s estimated that between 0.05 percent and 2 percent of people will experience anaphylaxis at some point during their lifetime.

At one point, researchers reported as many as 1,500 deaths caused annually by anaphylaxis in the United States.

Both the rate of anaphylaxis and the share of the population experiencing it have increased over the last few decades. This increase has been sharper among children and youth than in other age groups.

In just the past 15 years, the rate of hospital admissions for anaphylaxis caused by food allergies has multiplied by a factor of 5. (4)

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

In one study of children ages 0 to 17, when compared with non-Hispanic white children, African American children had significantly higher rates of allergies to wheat, soy, corn, fish, and shellfish. Hispanic children also had higher rates of allergies to corn, fish, and shellfish.

The same study found that African American and Hispanic children were at higher risk for adverse outcomes related to food allergies, including higher rates of anaphylaxis. This may be due, in part, to a higher rate of unrecognized food allergies. (8)

A separate analysis of emergency department visits in Florida from 2005 to 2006 for anaphylaxis found that Black people were more likely than other groups to have a food trigger for anaphylaxis, while white people were more likely to have it triggered by insect venom. (9)

Anaphylaxis is a severe allergic reaction and may be caused by different kinds of allergies, including the following:

• Food allergies
• Drug allergies
• Insect venom allergies
• Latex allergy (2)

In addition, untreated anaphylaxis can lead to serious or life-threatening health conditions, such as:

• Shock (sudden drop in blood pressure)
• Cardiac arrest (no heartbeat)
• Respiratory arrest (no breathing) (1)

The following organizations and websites offer more information on anaphylaxis and related conditions:

American Academy of Allergy, Asthma & Immunology (AAAAI)

This advocacy and research organization has information on allergy-related conditions and treatments on its website, along with resources to help you find an allergist or ask a health expert a question.

Asthma and Allergy Foundation of America (AAFA)

This nonprofit group is the leading patient-centered organization for people with asthma and allergies. Its website contains useful health information, as well as an overview of allergy-related research, news, and advocacy opportunities.

Seattle Allergy & Asthma Research Institute

This clinical research organization provides information on its ongoing and currently recruiting studies, including how to find out if you’re eligible to participate in one.

Benaroya Research Institute

This research institute focuses on disorders of the immune system, including autoimmune disorders and allergies. Its website has information on a variety of research projects, including how to participate.

Food Allergy Research and Education (FARE)

This patient advocacy and research organization has provided over $100 million in funding for food allergy research. Its website provides detailed information on living with food allergies, along with its research-based projects and priorities.

Kids With Food Allergies

This website from the Allergy and Asthma Foundation of America (AAFA) contains practical guidance on living with food allergies, including allergy alerts regarding specific products, how to find a local or online allergy support group, and allergy-friendly recipes.