Anaphylaxis

Anaphylaxis is a severe allergic reaction. It can progress into a life-threatening condition. Anaphylaxis is caused by an exposure or ingestion of something to which you are allergic. The immune system then over-reacts. 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 or ingestion of an allergen (a “trigger”). This triggers immunoglobulin E (IgE) antibodies. It 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. You may have swelling on your mouth, tongue or throat. 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.

Use epinephrine

Administer epinephrine at the first sign of symptoms. Using it right away can prevent symptoms from getting worse.

EPINEPHRINE FIRST, EPINEPHRINE FAST! 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, tongue, throat and airways
  • Feeling dizzy or faint
  • Loss of consciousness
  • Sudden drop of blood pressure, cardiac or respiratory arrest
A person wearing a gray top is clutching their chest, seemingly in discomfort or experiencing difficulty breathing, possibly due to anaphylaxis. Their face is partly visible, and their posture suggests concern.

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 minutes after being stung by a bee.

Infographic illustrating the average time to respiratory or cardiac arrest from anaphylaxis: food allergy takes 30 minutes, venom allergy 15 minutes, and medication allergy just 5 minutes. Source: Clinical & Experimental Allergy, Volume 30, Issue 8.
A man in a white shirt leans against a gray wall, covering his face with one hand, as if warding off the onset of anaphylaxis. His expression reveals distress or headache, underscoring the urgency of his situation.

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.

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 breathing problems 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 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)
  • Itch 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)

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.

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 a dose of epinephrine, but they may come back. This is what is known as a biphasic reaction – a second reaction. If you experience a biphasic reaction, you should seek emergency care after giving a second dose of epinephrine.

Two hands hold two epipens, one with a yellow cap and the other with an orange cap, against a white background. The auto-injectors have labels and instructions printed on them.

What is a biphasic reaction?

Sometimes you can have a rebound reaction involving anaphylaxis. This is called biphasic anaphylaxis. Biphasic means the symptoms come in two phases. You may recover from the first severe reaction with a dose of epinephrine, but symptoms may 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 a severe allergic reaction.

This is the main reason why you should:

  • Carry two epinephrine devices with you at all times if you are at risk.
  • Go to the emergency department if you experience a biphasic reaction.

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.

Infographic titled "Anaphylaxis At a Glance" with sections on allergens, symptoms, and emergency actions. Includes images of foods, a human outline showing symptoms, and EpiPen instructions. Logos for Allergy & Asthma Network and ARS.
Get a Free Copy of Anaphylaxis at a Glance

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.

A hand holding a Neffy nasal spray device with a white nozzle, blue label, and a rectangular shape. The spray is intended for medical use.

Epinephrine comes in a variety of devices and can be used at various doses based on weight.

Epinephrine Nasal Spray (neffy®)

Dosage (spray in nostril):

  • 2 mg for adults and children over 66 pounds

Epinephrine auto-injectors (EpiPen®, AUVI-Q® and generics)

Adult Dosage (injection in outer middle of thigh):

  • 0.3 mg for people over 66 pounds

Children’s Dosage (injection in outer middle of thigh):

  • 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 over 66 pounds)

After the first dose, monitor symptoms carefully. A second dose of epinephrine can be given if symptoms do not go away or they come back. If a second dose is given, go to the emergency department for additional treatment.

Once treated with epinephrine, aftercare focuses on treating and managing 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)

Remember, initial treatment for anaphylaxis always requires epinephrine.

Anaphylaxis: when to give epinephrine?

Give epinephrine at the first sign of an anaphylaxis emergency. If you aren’t sure if it’s anaphylaxis, give epi anyway! Epinephrine is generally safe and effective, even if given when not needed. It can cause side effects such as anxiety, dizziness, shakiness, headache, and nausea, but these are usually mild and not life-threatening.

Speak to your doctor about when to use epinephrine if you have certain pre-existing conditions. These include heart problems, high blood pressure, or diabetes.

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?

First, if you do not have epinephrine on hand to treat anaphylaxis, you should call 911, or go to the hospital, emergency department or urgent care clinic right away for treatment. Do not delay!

If your symptoms improve after a first dose of epinephrine and you’re feeling better, you do not need to go the hospital or emergency department.

However, you should call for emergency medical help or go to the hospital or clinic if…

  • symptoms return or worsen after the first dose of epinephrine.
  • you have severe anaphylaxis;
  • symptoms do not go away promptly or completely after the first dose of epinephrine;
Close-up of a gloved hand holding an EpiPen autoinjector with a yellow label. The label includes the words "0.3 mg Epinephrine Pen" and "Auto-Injector" along with usage instructions.

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.

How does epinephrine work?

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

Epinephrine is the ONLY drug that will reverse an 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.

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 devices at all times. This includes people with a history of food allergy, insect venom allergy, latex allergy, or other severe allergies.

Available devices include an epinephrine nasal spray and an epinephrine auto-injector.

Epinephrine needs to be used at the first sign of symptoms. Seek emergency medical care if symptoms return or worsen after the first dose of epinephrine.About 25% of people need a second dose to relieve symptoms. So it’s important to always carry two devices with you at all times.

Some studies show many parents are hesitant to give their child epinephrine using an auto-injector. The primary reason cited by parents is they are often fearful of hurting their child (or themselves) with the needle. For those parents, a needle-free option – the epinephrine nasal spray called neffy – is now available.

Some parents may be uncertain if their child is really having a dangerous allergic reaction. Remember, epinephrine is life-saving treatment for anaphylaxis and must be given without delay. There is no way to predict how severe an anaphylactic episode might become. The time to begin treatment is when symptoms first develop.

Epinephrine is not a dangerous drug. Adverse side effects typically are mild. Anaphylaxis, however, can be fatal – so it’s safer to treat it!

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

What is an Allergy and Anaphylaxis Emergency Plan?

An Allergy and Anaphylaxis Emergency Plan is a helpful tool to help you manage and treat anaphylaxis, especially in children. It includes information about the allergy and provides an outline of symptoms to watch for. It also offers information on how to give epinephrine. It’s an important tool for families, grandparents, caregivers and school staff. Ask your doctor to develop a plan for you or your chid.

A person carefully holds an EpiPen, their hands moving deftly to remove the blue safety cap. The device features a distinct yellow label and an orange tip, while a ring subtly adorns their left finger, reflecting light.

How do you use an epinephrine nasal spray?

Insert the nozzle of the nasal spray fully into one nostril. Hold the nasal spray straight into the nose. Do not angle it against the inside or outside wall, as this could cause you to lose some of the medication. Press the plunger firmly to activate the device and deliver the epinephrine. Avoid sniffing during and after taking the medicine.

The medication is given as a single dose.

It’s important to always carry two epinephrine nasal spray devices. You may need a second dose if your symptoms continue or come back.

If a second dose is needed, use a new nasal spray. Insert it into the same nostril you used for the first dose. Do not reuse the neffy you used for the first dose. The second dose should be taken at least five minutes after the first dose.

How do you use an epinephrine auto-injector?

Epinephrine auto-injectors contain a pre-measured dose of epinephrine. Different strengths are available for treating different body weights. There are several brands of epinephrine auto-injectors available. Each has its own instructions. Learn how to use the specific device you have. Check the website of the device you are using so you can view the training video.

Here are general instructions for using an epinephrine auto-injector:

Pull off the safety cap or needle covering if there is one. Inject the epinephrine into the outer thigh; avoid the buttocks area. (The needle is designed to go through clothing if necessary.) Hold the leg and keep it steady while you inject the epinephrine.

Once injected, follow the device’s instructions for how long to keep it in place – usually 2-3 seconds – until all the epinephrine is delivered. Then remove the device and massage the injection site for 10 seconds.

See “What is Epinephrine?” for detailed information.

Anaphylaxis Questions and Answers (Q&A)

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

If you suspect you or a loved one are experiencing anaphylaxis, it is crucial to act fast. Use epinephrine immediately and call 911 if symptoms persist or worsen.

If you also have asthma and you’re not sure if your symptoms are asthma or anaphylaxis, you should 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.

Remember, epinephrine is the first and primary treatment for anaphylaxis, not your asthma inhaler. It is important to be able to recognize symptoms of anaphylaxis and asthma. This way you will know whether you need epinephrine or your inhaler.

Follow up with your healthcare provider or an allergist to review your treatment plan.

Anaphylaxis puts your body into shock. It can cause a sudden drop in blood pressure, your airways can be blocked, your mouth or throat might swell up, and you could go into cardiac or respiratory arrest. It is a critical condition that can kill you within 15 minutes if left untreated.

In some cases, severe allergic reactions 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 vital to treat with epinephrine to prevent a tragic outcome.

Most cases begin within minutes of exposure, especially with an insect venom allergy. However, it may take a little longer with foods.

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

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.

Some people experiencing an anaphylactic reaction may have a drop in blood pressure (hypotension). But others 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.

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. There is no way of knowing if your mild symptoms will turn severe. All cases should be treated with epinephrine.

Yes, anaphylaxis can be fatal. Deaths are often related to a delay in giving epinephrine or not giving epinephrine at all.

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

Severe allergy risk factors 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 factors are 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 allergy.

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.

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.

Seizures from an anaphylactic reaction are not common, but they can happen on occasion.

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.

Yes, you can experience an anaphylactic reaction while you sleep and it can wake you up. Symptoms involving the respiratory system, digestive system and the heart can 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.

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. But they may not see a sudden drop in blood pressure that leads to anaphylactic shock.

Anyone experiencing mild anaphylaxis symptoms or anaphylactic shock should use epinephrine.

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 caused anxiety or stress.

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

Yes, it can occur without hives. Up to 20% of cases involve no skin symptoms.

There is no substitute for epinephrine in the event of an anaphylactic reaction. If you do not have epinephrine with you or it’s not readily available, dial 911 immediately for emergency medical help.

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.

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.

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.