What is Anaphylaxis?


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Anaphylaxis is a severe allergic reaction that can progress into a life-threatening condition. It is caused by an exposure to something to which you are allergic. Symptoms 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 certain foods, certain 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. 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?

Severe allergic reactions can occur after exposure to an allergen (a “trigger”). This triggers immunoglobulin E (IgE) antibodies and causes the immune system to flood the body with histamine 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, symptoms may cause you to lose consciousness and lead to a cardiac arrest, or even death.

The anaphylaxis timeline

Symptoms usually begin quickly after exposure to an allergen. They usually start within seconds to minutes. But sometimes symptoms may emerge 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
  • Swollen tongue or difficulty swallowing
  • Headache, sweating or dizziness

If you experience symptoms involving two or more body organs (skin, respiratory system, digestive system, heart), this is 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 symptoms from getting worse. Once you take 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 symptoms begin, you may at first just feel “off” – as if something in your body does not feel quite right. 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 or 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 a severe allergic reaction, certain foods, medications and insect venom account for 90% of anaphylactic reactions.

Within these groups, the most common triggers are:

  • Legumes (such as peanut)
  • Animal proteins (such as cow’s milk, egg, finned fish and shellfish)
  • Venom from stinging insects (such as bee stings, wasps and yellow jackets)
  • Venom from insect bites (such as fire ants)
  • Pain medications (such as aspirin or ibuprofen)

Tree nuts (such as almonds, walnuts, pecans and hazelnut), soy, wheat and sesame are other common triggers. Food allergy research reveals more than 170 different foods can trigger allergic reactions.

Antibiotics such as penicillin and amoxicillin are also common triggers. In rare cases, exposure to latex can trigger symptoms, too.

How fast can it 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?

Symptoms can be different each time a person experiences an anaphylactic reaction. They may vary in severity each time. Once symptoms start, they usually progress quickly.

Symptoms usually involve two or more organ system of the body. These can include:

  • Skin: itching, redness, swelling, hives
  • Mouth: swelling of lips, itchy throat, tongue
  • Digestive: nausea, vomiting
  • Respiratory: shortness of breath, wheezing, coughing, chest pain and/or tightness
  • Heart: drop in blood pressure, weak pulse, dizziness, faintness

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

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

You can have an allergic reaction that is not severe. 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

  • Nausea and vomiting

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


What is the difference between an allergic reaction and anaphylaxis?

With an anaphylactic reaction, you will have symptoms involving two or more body systems at the same time. You may have all of the symptoms at the same time, and they gradually become more severe.

With an allergic reaction, you will have one type of symptom – either have a rash OR be itchy OR have an upset stomach.

If you are not sure what your symptoms are, assume it’s an anaphylactic reaction. Remember, if you wait too long, you may not be able to stop severe symptoms.

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?

Symptoms normally peak within a half-hour of exposure, but they can last for several hours. About 20% of the time, you can get your symptoms under control with treatment, but they may come back. This is what is known as a biphasic reaction – a second 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. This is called biphasic anaphylaxis. Biphasic means the symptoms come in two phases. You may recover from the first reaction, but symptoms come back. This can occur up to 12 hours after your first symptoms. 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.
  • Go to the emergency room after using epinephrine.


What is anaphylactic shock?

Anaphylactic shock is an allergic emergency. It refers to the narrowing of the airways and a drop in blood pressure in response to exposure to an allergen. The treatment is epinephrine first, epinephrine fast, whether shock is present or not.

How common is anaphylaxis?

It occurs in about 1 in 50 people. Some believe the rate is even higher. So while the condition is still quite rare, it is very important to be aware of the risk if you live with severe allergies.

Are cases on the rise? Data suggests that food-related anaphylaxis is increasing, particularly in children and adolescents. Experts aren’t sure if it’s now more common or if more people are recognizing it and getting help.

Who is at risk of anaphylaxis?

Anyone with a severe or life-threatening allergy is at risk, especially if there is an undiagnosed allergy. People most at risk are those with a history of allergies and asthma. People with a family history of anaphylaxis are at increased risk. Anyone who has experienced an anaphylactic reaction in the past is at risk for future reactions.

Woman pulling cap off practice auto-injector

What is the treatment for anaphylaxis?

Epinephrine is the first line of treatment. 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 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, 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)

This additional care helps with symptom management. Remember, 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 an anaphylactic reaction, you need to go to the hospital right away or call 911 for an ambulance. You should go even if your symptoms improve after administering epinephrine.

You should also call 911 if you don’t have epinephrine to treat an anaphylactic reaction.

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 an anaphylactic reaction. Epinephrine is typically given using an auto-injector. It injects the medicine 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 anaphylactic reaction. It should be given as soon as symptoms appear.

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

Can antihistamines like Benadryl® stop anaphylaxis?

Antihistamines do not stop anaphylaxis. Doctors urge use of an epinephrine auto-injector as the first treatment of any severe allergic reaction. Epinephrine will not harm a patient.

Antihistamines only treat a few minor anaphylactic symptoms – such as 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?

Can you prevent anaphylaxis? Yes, you can avoid triggers. Don’t buy or serve foods containing your allergens. Tell doctors about medications to which you are allergic. Stay away from areas where there are stinging insects as best you can. Keep away from products containing latex. Talk with a healthcare provider about other strategies to avoid allergens.

Sometimes accidental exposures occur, though. People at risk should carry two epinephrine auto-injectors at all times. This includes people with a history of food allergy, insect venom allergy, or other severe allergies.

The epinephrine auto-injector needs to be used at the first sign of symptoms. Then you should seek follow-up medical care right away. About 25% of people need a second dose of epinephrine to relieve their symptoms, so it’s important to always carry two with you at all times. In addition, sometimes an epinephrine auto-injector can malfunction, so having a second device on hand is beneficial.

Some studies show many parents are hesitant to give their child epinephrine. The primary reason cited by parents is they are often fearful of hurting their child (or themselves). Sometimes they are uncertain if their child is really having a dangerous allergic reaction.

Remember, epinephrine is life-saving treatment and must be given without delay. There is no way to predict how severe an anaphylactic episode might become, so the time to begin treatment is when symptoms first develop. Epinephrine is not a dangerous drug. Adverse side effects typically are mild and affect only elderly and frail patients. Anaphylaxis, however, can be fatal — it’s safer to treat!

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

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.

What should I do if I’m not sure my symptoms are anaphylaxis or asthma?

If you suspect you are experiencing anaphylaxis, it is crucial to act fast. Use epinephrine immediately and call 911 if symptoms persist. If you also have asthma and you’re not sure if your symptoms are asthma or anaphylaxis, you should still administer epinephrine first as it has benefits for both conditions. If your symptoms do not improve with epinephrine and you think asthma is the cause, then use your quick-relief inhaler for asthma. But remember, epinephrine is the first and primary treatment for anaphylaxis, not your asthma inhaler. It is important to learn to recognize the symptoms of anaphylaxis and asthma so you know whether you need epinephrine or your inhaler. Follow up with your healthcare provider or an allergist to review your Allergy and Anaphylaxis Emergency Plan.

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, severe allergic reactions may resolve without treatment. But, remember delayed treatment is the main cause of death. 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 begin within minutes of exposure, especially an insect sting allergy. However, it may take a little longer with foods.

Can anaphylaxis be delayed?

Most symptoms come on quickly. However, there are cases of delayed anaphylaxis, particularly associated with an allergy to meat (beef, pork, lamb). Allergy symptoms occur after a tick bite and is known as Alpha Gal Syndrome. Symptoms happen hours after eating a meal. People who experience a meat allergy often don’t realize it’s a food-allergic reaction until they are diagnosed.

Can you get anaphylaxis from touching an allergen?

It is highly unlikely to have an anaphylactic reaction simply by touching an allergen – this includes food and medication. 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 the allergen), then it may trigger a severe allergic reaction.

The exception is latex. Putting on a latex glove or touching anything that contains latex (such as balloons, rubber bands, Band-aids, mouse pads or bathmats) may trigger a severe allergic reaction in some people. If you have latex allergy, it’s best to avoid latex.

Can anaphylaxis cause high blood pressure?

Most people experiencing an anaphylactic reaction may have a drop in blood pressure (hypotension). But some may have their blood pressure go up (hypertension). You cannot tell if someone is experiencing a severe allergic reaction just by their blood pressure reading.

Can anaphylaxis be mild?

Yes, symptoms can be mild. But remember, an anaphylactic reaction means more than two body systems are affected (skin, lungs, stomach, heart). Severe symptoms can arise without warning, and there is no way of knowing if your mild symptoms will turn severe. All cases should be treated with epinephrine and follow-up medical treatment.

Can anaphylaxis kill you?

Yes, this condition can kill you. Deaths are usually related to a delay in administration of epinephrine or not administering epinephrine at all.

Who is at greatest risk for fatal anaphylaxis?

Everyone is at risk. However, people who have severe allergies are at higher risk. Most cases of anaphylaxis occur in people between the ages of 30 and 39.

Severe allergies are more prevalent in certain age groups:

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

Anaphylaxis risk is also more prevalent in certain age groups:

  • Boys 0-19 years of age are at higher risk than girls in the same age range.
  • Slightly more adolescent and teenage girls are at greater risk than boys of the same ages.
  • Women between 40-49 are at higher risk than men in this age group.

People diagnosed with both asthma and food allergy are at higher risk for anaphylaxis than those with just food allergies.

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

Adolescents, teens and young adults with both asthma and food allergy also face a higher risk of death. 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 from an anaphylactic reaction are not common, but they can happen on occasion.

Can I get anaphylaxis when pregnant?

Anaphylaxis during pregnancy is rare but it can happen. It poses both a risk to mother and child, so treatment is critical. Pregnancy is no reason to avoid epinephrine.

Will anaphylaxis wake you up?

Yes, you can experience an anaphylactic reaction while you sleep. Symptoms involving the respiratory system, digestive system and the heart 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. If you think your child is having an allergic reaction, don’t send your child to bed until it is clear that symptoms have passed.

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 symptoms or anaphylactic shock should use epinephrine and get emergency medical help.

Can anxiety cause anaphylactic shock?

This is very rare, but there are reported cases where anxiety or stress may have caused an anaphylactic reaction. More likely, it is that symptoms of anaphylaxis have caused anxiety or stress.

Anaphylaxis is caused by what body system?

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

Can I have anaphylaxis without hives?

Yes, it can occur without hives. Up to 20% of cases 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 and do not have epinephrine with you.

Can I get anaphylaxis with no known cause?

You may have heard of people that develop anaphylactic symptoms for no apparent reason. This is rare, but it is a condition known as idiopathic anaphylaxis. This is the diagnosis when there is no known cause to symptoms. People who have idiopathic anaphylaxis should be evaluated by an allergy specialist. Allergy testing may be necessary to determine triggers.

What is an anaphylactoid reaction?

An anaphylactoid reaction is identical to anaphylaxis but no IgE antibodies are involved. Anaphylactoid reactions are sometimes referred to as anaphylactic-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.