Anaphylaxis is a severe allergic reaction. Foods, insect bites, and other factors can cause it. Symptoms include swelling, hives, and difficulty breathing. These can progress quickly to become anaphylactic shock, which can be fatal.

Each year, there are 200,000 hospital visits due to food allergies in the United States, according to the Asthma and Allergy Foundation of America (AAFA).

People also commonly have allergic reactions to medications and insect stings.

The AAFA report that more than 50 million people in the U.S. have an allergic reaction each year and that allergies are the sixth leading cause of chronic illness in the country.

Below, we describe what a severe allergic reaction — a condition called anaphylaxis — feels like and what to do if it happens. We also explore the causes and what goes on in the body during this reaction.

Anaphylaxis happens when the body reacts to a foreign substance as if it were a serious threat to health.

The most common triggers for these reactions are medications, foods, and insect stings.

Some foods that often trigger allergic reactions include:

  • milk
  • eggs
  • fish
  • crustacean shellfish
  • wheat
  • soy
  • peanuts
  • tree nuts

Any substance that causes an allergic reaction is called an allergen. For some people, even minimal exposure to traces of an allergen can cause a severe reaction.

In its reaction to an allergen, the body produces large amounts of histamine — a signaling molecule that can trigger an inflammatory response.

This response can lead to:

  • dilation of the blood vessels
  • a sudden drop in blood pressure
  • loss of consciousness
  • shock

In a person experiencing anaphylaxis, the airways often become narrow, making breathing difficult.

In addition, the blood vessels may leak, causing edema, a type of swelling that results from the accumulation of fluid.

The reaction may happen immediately after contact with the allergen or within hours of contact. Very occasionally, it happens days later.

The symptoms of anaphylaxis can signal that urgent medical attention is required.

Each individual’s specific symptoms will depend on the type of allergy and the trigger, but they may include:

  • nasal congestion
  • an itchy mouth or throat
  • a full, heavy feeling in the tongue
  • trouble swallowing or a feeling that something is stuck to the tongue or throat
  • a cough
  • a hoarse voice
  • wheezing
  • shortness of breath and tightness in the throat
  • difficulty breathing
  • chest pain
  • stomach pain and cramps
  • nausea and vomiting
  • diarrhea
  • swelling and itchiness of the skin, which may be warm and red, with hives or another rash
  • anxiety and a feeling of impending doom
  • swelling of the feet, hands, lips, eyes, and sometimes the genitals
  • low blood pressure and poor circulation, leading to pale blue skin
  • a low pulse, dizziness, or faintness
  • shock
  • loss of consciousness

The person may also have itchy, red, watery eyes, a headache, and cramping of the uterus. They may have a metallic taste in their mouth.

Severe breathing difficulties, a significant drop in blood pressure, or both can lead to shock, which can be fatal.

Anaphylaxis: Symptoms and what to do

Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:

  • hives
  • swelling of the face or mouth
  • wheezing
  • fast, shallow breathing
  • a fast heart rate
  • clammy skin
  • anxiety or confusion
  • dizziness
  • vomiting
  • blue or white lips
  • fainting or loss of consciousness

If someone has these symptoms:

  1. Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.
  2. Dial 911 or the number of the nearest emergency department.
  3. Lay the person down from a standing position. If they have vomited, turn them onto their side.
  4. Stay with them until the emergency services arrive.

Some people may need more than one epinephrine injection. If the symptoms do not improve in 5–15 minutes, or they come back, use a second pen if the person has one.

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Anyone who experiences a severe allergic reaction requires urgent medical attention.

First aid for anaphylaxis includes the following steps:

  1. Remove the allergen, if possible, and call for emergency assistance.
  2. Keep the person cool and loosen any constrictive clothing.
  3. If they feel faint, get them to sit, recline, or lie flat.
  4. Ask if the person has a history of allergic reactions.
  5. Help them administer any allergy medication that they carry.
  6. Reassure the person, and stay with them until emergency aid arrives.

If the person has a history of severe reactions, they may be carrying an adrenaline, or epinephrine, injection kit. It may contain an auto-injector, such as an EpiPen.

The injector will provide a dose of epinephrine, a form of adrenaline.

Experts recommend that some people with allergies carry two injectors at all times.

If a child needs the medication, calm them first, and ensure that they are still. This will leave both hands free to operate the device.

When using an EpiPen injector, it is essential to:

  1. Remove the pen from the carrying case.
  2. Hold the injector in one fist, with the orange end pointing down.
  3. Remove the blue safety release with the other hand — in a straight upward motion, without bending or twisting sideways.
  4. Swing the hand carrying the device out to the side and push the orange end firmly against the outer thigh, at a right angle to the leg.
  5. Listen for a click as the needle comes through the orange end of the device, administering the dose.
  6. Hold the needle in place for at least 3 seconds.

After the dose is administered, the orange end will cover the needle and the window of the device will be blocked. If the needle tip is still visible, do not reuse the needle.

Never flip off the blue safety release with a thumb — always use two hands to prepare the injector.

Removing the safety release incorrectly can cause the injector to release its contents too early. As a result, there may be no medication in the device when the person administers it.

There are different types of injector. While they generally work in the same way, the instructions for each type may be slightly different.

The links below provide specific instructions for different injectors:

While waiting for help, ensure that the person can breathe. To make breathing easier, the person should be sitting up and leaning forward a little.

However, if they feel faint, they should be lying flat with their legs raised.

If the person faints, make sure that their head is tilted back and that they can breathe.

Stay with the person and monitor their condition until a healthcare professional arrives. When they do, explain, if possible:

  • what caused the reaction
  • whether the person has received any medication

If possible, make sure that the triggering allergen is as far from the person as possible. It should not accompany them to the hospital.

If the person stops breathing, administer cardiopulmonary resuscitation (CPR). The chest compressions should continue until professional help arrives.

If multiple people at the scene can administer CPR, they can take turns.

Here, learn CPR step by step with a visual guide.

Emergency treatment for a person with a severe allergic reaction involves an injection of epinephrine, or adrenaline.

Epinephrine helps in several ways:

  • It causes the blood vessels to constrict, decreasing swelling and helping to increase blood pressure.
  • It relaxes the muscles around the lungs.
  • It limits the reaction by blocking the body’s release of additional chemicals.

Most people respond well to this treatment, and symptoms usually start to subside right away. If there is no immediate improvement, the person will need another dose after 10 minutes.

Sometimes, symptoms of the reaction return after subsiding. The person may need to remain under observation in a hospital for 24 hours.

If an allergic reaction is less severe, a doctor may administer corticosteroid or antihistamine injections.

Anaphylaxis is a life threatening emergency. A person may experience this reaction to something that had never affected them before.

Allergic reactions are unpredictable, and it is crucial to avoid any known allergens, even if they have never caused severe reactions.

However, it is not always possible to avoid all allergens. A person may need to carry medication and wear a bracelet that makes their allergies clear.

If a person has a history of allergic reactions, it is important to describe the triggers to friends, family members, and employers or school staff.

Anaphylaxis is a potentially life threatening emergency. Anyone who experiences this severe allergic reaction requires immediate medical attention.

Knowing what to do in this situation may help save the person’s life. It is crucial to be aware of the symptoms and how to respond.