What is Anaphylaxis?


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Anaphylaxis is an extreme and life-threatening condition. It is a severe allergic reaction caused by an exposure to something to which you are allergic. Symptoms of anaphylaxis involve multiple body systems including the skin, heart, stomach and airways.

Between 1.6% and 5.1% of people in the United States have experienced at least one episode of anaphylaxis. The most common triggers are foods, medications and insect stings.

Anaphylaxis is an allergy emergency that can cause death in less than 15 minutes. Epinephrine is the only medication that can reverse symptoms of anaphylaxis. It is crucial to use epinephrine first and epinephrine fast. Then seek prompt treatment in your nearest emergency room.

What is anaphylaxis caused by?

Anaphylaxis occurs when symptoms affect two or more body systems. It is caused by your immune system flooding your body with chemicals to fight off an allergen. These chemicals often work fast to trigger a cascade of allergy symptoms.

Common anaphylaxis triggers are usually caused by a reaction to one of the following:

Anyone at risk for anaphylaxis can have a life-threatening allergic reaction – even if previous reactions were mild.

What happens during anaphylaxis?

Anaphylaxis is a severe allergic reaction caused by an exposure to an allergen (a “trigger”). These severe allergic reactions cause the immune system to flood the body with histamines and other chemicals in an attempt to fight the allergen.

This sudden chemical release can lead to shock. Your blood pressure may drop rapidly and your pulse may become fast and weak. Your airways may narrow or fill with fluids, making it hard to breathe. You may develop a skin rash and itching. Your stomach may cramp and you may experience vomiting and diarrhea.

Left untreated, these symptoms may cause you to lose consciousness and lead to a cardiac arrest, or even death.

The anaphylaxis timeline

Anaphylaxis usually begins quickly after exposure to an allergen. Initial symptoms usually start within seconds to minutes, but sometimes they may start up to two hours after exposure. A typical timeline may look like this:

Exposure to trigger

You swallow, inject or inhale an allergen.

Early symptoms

Early symptoms begin within seconds to minutes (sometimes it takes longer). They may include:

  • Hives or red, itchy skin

  • Cough, chest tightness, or trouble breathing

  • Stomach pain and/or nausea, vomiting, or diarrhea

  • Difficulty swallowing

  • Headache, sweating or dizziness

If you experience symptoms involving two or more body organs (skin, respiratory system, digestive system, heart), it’s anaphylaxis and you should administer epinephrine.

Inject epinephrine

Use your self-injectable epinephrine as soon as you feel symptoms. Using it right away can prevent anaphylaxis symptoms from getting worse. Once you have taken epinephrine, seek emergency care.

Any delay in administering epinephrine greatly increases the chance of hospitalization. Delaying or failing to use epinephrine has been associated with fatalities.

Without epinephrine, you could develop severe symptoms, including:

  • Difficulty breathing, wheezing, or airway blockage
  • A racing and weak pulse, low blood pressure, or abnormal heart rhythm
  • Severe swelling, including swelling of the mouth, throat and airways
  • Feeling dizzy or faint
  • Loss of consciousness
  • Sudden drop of blood pressure, cardiac or respiratory arrest

Young adult woman in grey shirt holding her hand to her throat and struggling to breathe because she's having an anaphylaxis episode

What does anaphylaxis feel like?

When anaphylaxis begins, you may at first just feel “off.” Your throat and skin may feel itchy and you may start to cough. You may feel your heart beat faster or feel light headed. Your stomach may begin cramping. You may feel like you have to throw up or have diarrhea. Some of these symptoms may suddenly get worse. You may feel like you can’t breathe, feel like you are going to pass out. Your skin may become pale. You may feel a sudden feeling of doom or extreme fear. This severe reaction can take just minutes.

What are the 5 most common triggers for anaphylaxis?

While any allergen can cause anaphylaxis, insect venom, foods and medications account for 90% of anaphylactic reactions.

Within these groups, the most common triggers for anaphylactic symptoms are:

  • Legumes (such as peanut)
  • Animal proteins (such as milk, egg, finned fish and shellfish)
  • Wasp stings
  • Bee stings (such as yellow jackets) or insect bites (such as fire ants)
  • Pain medications (such as aspirin or ibuprofen)

Antibiotics such as penicillin can also lead to anaphylaxis. In rare cases, exposure to latex can trigger anaphylaxis.

How fast can anaphylaxis happen? Most anaphylactic reactions begin within minutes of exposure to an allergen. However, in some cases the reaction can take a half hour or longer.

NOTE: Severe reactions can start out with mild symptoms and quickly get worse. Deaths from anaphylaxis have occurred 30 minutes after eating a food allergen and 15 after being stung by a bee.
Graphic of average time for anaphylactic shock/arrest

Man in white Tshirt holding his head and  leaning against a wall showing signs on an anaphylaxis episode

What are anaphylaxis symptoms?

The signs and symptoms can be different each time a person has anaphylaxis and may vary in severity each time. Once symptoms start, they usually progress quickly.

Signs and symptoms usually involve two or more organ system of the body. These can include:

  • Skin: itching, redness, swelling, hives
  • Mouth: itching, swelling of lips, itchy throat, tongue
  • Stomach: vomiting, diarrhea, cramps
  • Respiratory: shortness of breath, wheezing, coughing, chest pain and/or tightness
  • Heart: drop in blood pressure, weak pulse, dizziness, faintness
  • Headache, nasal congestion, watery eyes, sweating
  • Confusion, feeling of impending doom
  • Loss of consciousness

While skin symptoms, such as an itchy rash or hives, are common with anaphylaxis, they do not always occur. Ten to 20 percent of the time, anaphylaxis will occur with no skin symptoms.

How can you tell the difference between an allergic reaction and anaphylaxis?

Anaphylaxis is a severe allergic reaction. But you can have an allergic reaction that is not anaphylaxis.

Common symptoms of an allergic reaction include:

  • Sneezing and itchy, stuffy or runny nose (allergic rhinitis)

  • Itchy around the nose, mouth, eyes or roof of mouth

  • Itchy, red, watery or swollen eyes (allergic conjunctivitis)

  • Facial swelling, swollen lips, tongue (angioedema)

  • Itchy skin

  • Skin rashes (allergic contact dermatitis, eczema)

  • Hives

  • Cough

  • Wheezing

  • Breathing difficulties or shortness of breath

  • Headache

  • Nausea and vomiting

  • Asthma symptoms or asthma attack (if you have allergic asthma)


What is the difference between an allergic reaction and anaphylaxis?

With anaphylaxis, you will have several symptoms at the same time. With an allergic reaction, you will have a rash OR be itchy OR have an upset stomach. With anaphylaxis, you may have all of these symptoms at the same time, and they become more severe. If you are not sure if it’s an allergic reaction or anaphylaxis, assume it’s anaphylaxis. Remember if you wait too long, you may not be able to stop anaphylaxis.

How can you tell if your throat is closing up?

You may suddenly feel that your throat is tight or you have difficulty swallowing. You may have a hoarse voice or feel like you can’t breathe in air. This is a sign of an emergency, so use epinephrine and dial 911.

How long does anaphylaxis last?

Anaphylaxis symptoms normally peak within a half hour of exposure, but symptoms can last for several hours. About 20% of the time, you can get your symptoms under control with treatment, but the symptoms can come back. This is what is known as a biphasic reaction. This is why it is important to seek emergency care after using epinephrine.

Woman's hands holding two autoinjectors of epinephrine

What is a biphasic reaction?

Sometimes you can have a rebound reaction, or biphasic reaction. Biphasic means the symptoms come in two phases. It means you recover from anaphylaxis, but symptoms come back. This can occur up to 12 hours after your first symptoms of anaphylaxis. The rebound may be milder, but you may still need a second dose of epinephrine.

⚠ It’s important not to leave someone alone following an allergic reaction.

This is the main reason why you should:

  • Carry two epinephrine auto-injectors with you at all times if you are at risk for anaphylaxis.
  • Go to the emergency room after using epinephrine.

What is anaphylactic shock?

Anaphylaxis and anaphylactic shock are terms that people use when they refer to anaphylaxis. But not all anaphylaxis results in shock. Anaphylactic shock is an allergic emergency. It refers to a drop in blood pressure and narrowing of the airways in response to the exposure to an allergen. Anaphylaxis is treated with epinephrine first, epinephrine fast, whether shock is present or not.

How common is anaphylaxis?

Research shows that anaphylaxis occurs in about 1 in 50 people. Some believe the rate is even higher. So while the condition is still quite rare, it is really important for those living with allergies to be aware of the risk.

Is anaphylaxis on the rise? The data suggests that food-related anaphylaxis is increasing, particularly in children and adolescents. Experts aren’t sure if anaphylaxis is now more common or if more people are recognizing it and getting help. But either way, it is worth noting, particularly if you have a child with food allergies.

Who is at risk of anaphylaxis?

Potentially anyone is at risk of anaphylaxis, especially if there is an undiagnosed allergy. However, those most at risk are people with a history of allergies and asthma. People with a family history of anaphylaxis are also at increased risk. And anyone with a anaphylactic reaction in the past is at risk for future reactions.

Woman pulling cap off auto-injector

What is the treatment for anaphylaxis?

Epinephrine is the first line of treatment for anaphylaxis. It’s the ONLY medication proven to stop a life-threatening allergic reaction. Epinephrine needs to be given right away when you notice symptoms. Most epinephrine medications are self-injectable.

Epinephrine can be used in a variety of situations and at various doses. The epinephrine dose to treat anaphylaxis is:

Adult Dosage:

  • 0.3-0.5 mg intramuscularly (IM) or subcutaneously

Children’s Dosage is weight based:

  • 0.10 mg (for children 16.5 to 33 pounds) — AUVI-Q brand only
  • 0.15 mg (for children under 66 pounds)
  • 0.3 mg (for children and adults over 66 pounds)

A second dose of epinephrine can be given as needed, but each dose requires care monitoring.Once treated with epinephrine, anaphylaxis aftercare focuses on treating symptoms. Additional care may include:

  • Supplemental oxygen
  • Intravenous fluids and medications (such as antihistamines and cortisone to help with inflammation)
  • Albuterol (to help with wheezing or other respiratory symptoms)

And remember, this additional care does not help reverse anaphylaxis, but rather helps with symptom management. Treatment always requires epinephrine.

Anaphylaxis: when to give epinephrine?

Give epinephrine at the first sign an anaphylactic emergency. If you aren’t sure, give it anyway!

Any delay in administering epinephrine greatly increases the chance of hospitalization. Delaying or failing to use epinephrine has been associated with fatalities.

Anaphylaxis: when to go to hospital or when to call 911?

Any time you experience anaphylaxis, you need to go to the hospital. You should administer epinephrine and head to the hospital or call 911. You should go even if your symptoms improve after administering epinephrine. Call 911 if you don’t have epinephrine or if you develop severe symptoms, include trouble breathing and feeling faint.

Close-up of hand wearing a blue surgical glove is holding an epinephrine pen auto injector

What is epinephrine?

Epinephrine is a form of adrenaline, a hormone that naturally occurs in the body. It is also used as a life-saving medication to treat anaphylaxis. Epinephrine is given using an auto-injector or injection into the muscle in the outer thigh.

How does epinephrine work?

When injected, epinephrine stops the immune response to your allergen. Epinephrine relaxes the muscles in your airways, and also increases your heart rate and blood pressure.

Epinephrine is the ONLY drug that will reverse or prevent anaphylaxis. It should be given as soon as symptoms appear.

Any delay in giving epinephrine greatly increases the chance of hospitalization. Deaths due to anaphylaxis are often associated with either delaying the use of epinephrine or not using it at all.

Can antihistamines like Benadryl® stop anaphylaxis?

Antihistamines will not reverse anaphylaxis. Doctors recommend using an epinephrine auto-injector as the first treatment at the sign of any severe allergic reaction. Epinephrine will not harm a patient.

Antihistamines only treat a few minor symptoms of anaphylaxis – like hives. Antihistamines take about 30 or more minutes to take effect, which is far too long to treat an urgent medical condition.

Don’t wait. Don’t delay giving epinephrine. One more time: epinephrine will treat a life-threatening allergic reaction – antihistamines will not.

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What to do if you are at risk for anaphylaxis?

People at risk for anaphylaxis should carry two epinephrine auto-injectors at all times. This includes people with a history of food allergy, insect venom allergy, or other allergies. The epinephrine auto-injector needs to be used at the first sign of symptoms and seek follow-up medical care right away. About 25% of people need a second dose of epinephrine to relieve their symptoms. Sometimes an epinephrine auto-injector can malfunction or you may require a second dose, so it’s important to always carry two with you at all times.

Studies show many parents are hesitant to give their child epinephrine. They are often fearful of hurting their child (or themselves) as the primary reason. Sometimes they are uncertain if their child is having a dangerous allergic reaction. Parents need to remember that epinephrine is the life-saving treatment for a severe allergic reaction and must be given without delay.

It may be a good idea to wear a medical bracelet identifying that you are at risk of anaphylaxis. This can help EMTs and ER doctors diagnose your condition more quickly and provide treatment.

Studies show that many parents are hesitant to give their child epinephrine. They are often fearful of hurting their child (or themselves) as the primary reason. Sometimes they are uncertain if their child is having a dangerous allergic reaction. Parents need to remember that epinephrine is the life-saving treatment for a severe allergic reaction and must be given without delay.

What is an Allergy and Anaphylaxis Emergency Plan?

A helpful tool when it comes to managing and treating anaphylaxis, especially in children, is an Allergy and Anaphylaxis Emergency Plan. This is a plan that includes information about a child’s allergy, asthma, and provides an outline of symptoms to watch for and how to give epinephrine. It is an important tool for families, grandparents, caregivers and school staff. Parents should ask their doctor for a completed plan.

Woman opening auto-injector case

How do you use an epinephrine auto-injector?

Epinephrine auto-injectors contain a pre-measured dose of epinephrine. Two different strengths are available for treating different body weights.

There are several different brands of epinephrine auto-injectors available. Each has its own operating instructions. Be sure to visit the website of the device you are using so you can view the training video and learn how to operate the specific device you have.

Some epinephrine treatments are available as an auto-injector while some are a pre-filled syringe. Be sure you know what your prescribed device is.

See “What is Epinephrine?” for detailed information.

Q&A icon

Anaphylaxis Questions and Answers (Q&A)

Here are some popular questions regarding Anaphylaxis that people often ask. We also have a page on Anaphylaxis Statistics.

Why is anaphylaxis considered a critical situation?

Anaphylaxis puts your body into shock. It can cause a sudden drop in blood pressure, your airway can be blocked, and all this can cause a cardiac or respiratory arrest. It is a critical condition that can kill you within 15 minutes if left untreated.

Can anaphylaxis go away on its own?

In some cases, anaphylaxis may resolve without treatment. But, remember delayed treatment is the main cause of death from anaphylaxis. So, rather than use a “wait and see” approach, it is crucial to treat with epinephrine to prevent a tragic outcome.

Can anaphylaxis come on slowly?

Most cases of anaphylaxis begin within minutes of exposure, especially an allergy to stinging insects. However, it can take a little longer with foods.

Can anaphylaxis be delayed?

Most anaphylaxis symptoms come on quickly. However, there are cases of delayed anaphylaxis, particularly associated with an allergy to meat (beef, pork, lamb). This condition is known as Alpha Gal Syndrome.

Can you get anaphylaxis from touching an allergen?

It is highly unlikely to experience anaphylaxis by simply touching an allergen – including food. However, if the allergen gets in contact with a mucus membrane (such as if you put your fingers into your mouth or nose after touching an allergen), then it may trigger a severe allergic reaction.

Can anaphylaxis cause high blood pressure?

Most people with anaphylaxis experience a drop in blood pressure (hypotension). But some people with anaphylaxis may have their blood pressure go up (hypertension). You can’t tell if someone is having anaphylaxis just by their blood pressure reading.

Can anaphylaxis be mild?

Remember that anaphylaxis means more than two body systems are affected (skin, lungs, stomach, heart). Even if the reaction is mild, having multiple body systems affected at the same time means you are having anaphylaxis. You need epinephrine and medical help immediately.

Can anaphylaxis kill you?

Yes, anaphylaxis can kill you. Deaths due to anaphylaxis are usually related to a delay in administration of epinephrine.

Who is at greatest risk for fatal anaphylaxis?

Everyone is at risk for anaphylaxis. However, some are at higher risk, particularly those who have severe allergies. Most cases of anaphylaxis occur in people between the ages of 30 and 39. Cases are broken down this way:

  • Food-related anaphylaxis is most common in children ages 0-9 years.
  • Insect venom anaphylaxis is most common in adults ages 20-39 years.
  • Medication-related anaphylaxis is most common in adults ages 30-39 years.

More boys in the 0-19 age range experienced anaphylaxis than girls in the same age range. However, slightly more adolescent and teenage girls experienced anaphylaxis than boys of the same ages. Women between 40-49 were more likely to have anaphylaxis than men in this age group.

When it comes to fatal anaphylaxis, studies show adolescents, teenagers and young adults with food allergies are at highest risk of death from anaphylaxis. This may be due in part to risk-taking behavior common in that age group, hormones, or a reluctance to carry epinephrine auto-injectors.

People diagnosed with both asthma and food allergy are at higher risk for anaphylaxis than those with just food allergies. Adolescents, teens and young adults with both asthma and food allergy also face a higher risk of death from anaphylaxis. The key message for parents is to help children understand their asthma and food allergy so that when they are older, they know how to self-manage their condition.

Can anaphylaxis cause seizures?

Seizures are not common with anaphylaxis, but they can happen on occasion.

Can I get anaphylaxis when pregnant?

Anaphylaxis during pregnancy is rare but it does happen. And pregnancy is no reason to avoid epinephrine. In fact, anaphylaxis during pregnancy poses both a risk to mother and child, so treatment is crucial

Will anaphylaxis wake you up?

Can you have anaphylaxis while you sleep? The answer is yes, but the symptoms should wake you up. If you have a child with food allergies, you may worry that your child won’t be able to let you know there is a problem. Avoid feeding new foods right before bedtime. And if you think your child is having an allergic reaction, don’t send him or her to bed.

Are anaphylaxis and anaphylactic shock the same?

Anaphylaxis and anaphylactic shock are often referred to as the same. But they are not always the same. Some people may experience a mild anaphylactic reaction and not go into shock. For example, they may experience hives and difficulty breathing after accidentally eating a food allergen. They may not see a sudden drop in blood pressure that leads to anaphylactic shock. Anyone experiencing mild anaphylaxis or anaphylactic shock should use epinephrine and get emergency medical help.

Can anxiety cause anaphylactic shock?

There have been cases where anxiety or stress may have caused anaphylaxis. More likely, it is that anaphylaxis may cause stress and anxiety in some people. Anyone who has experienced anaphylaxis should make an appointment with an allergy specialist. They can perform allergy testing, diagnosis, and treatment.

Anaphylaxis is caused by what body system?

Anaphylaxis is caused by your immune system. However, it can effect multiple body systems. This includes your cardiac, respiratory, gastrointestinal, and skin systems.

Can I have anaphylaxis without hives?

You can have anaphylaxis without hives. Up to 20% of cases of anaphylaxis involve no skin symptoms.

What can I use if I don’t have an EpiPen® or epinephrine auto-injector?

There is no substitute for epinephrine in the event of an anaphylactic reaction. So you should dial 911 immediately if you develop symptoms of anaphylaxis and do not have epinephrine with you.

Can I get anaphylaxis with no known cause?

You may have heard of people that develop anaphylaxis for no reason. This is rare, but it is a condition known as idiopathic anaphylaxis. People who have experienced anaphylaxis should be evaluated by an allergist for allergy testing. But, in rare cases, there may not be a known cause.

What is an anaphylactoid reaction?

Anaphylaxis is an allergic reaction triggered by the presence of IgE antibodies in the body. An anaphylactoid reaction is identical to anaphylaxis but no IgE antibodies are involved.

Anaphylactoid reactions are sometimes referred to as anaphylaxis-like reactions. The term anaphylactoid is not frequently used since the symptoms and treatment are the same as for anaphylaxis.

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Reviewed by:
Purvi Parikh, MD, FACAAI is an adult and pediatric allergist and immunologist at Allergy and Asthma Associates of Murray Hill in New York City. She is on faculty as Clinical Assistant Professor in both departments of Medicine and Pediatrics at New York University School of Medicine.