What is anaphylaxis?

Woman on her cell phone looking serious and pointing towards the camera. Her message? In the event of anaphylaxis call 911

Anaphylaxis is a sudden and severe systemic allergic reaction which can be life-threatening. Common triggers are food, insect venom, medicines and latex. If you have these allergies, your doctor will talk to you about the symptoms of anaphylaxis and what to do if you spot them. It’s a medical emergency.

Studies from around the world suggest anaphylaxis could affect up to 5% of people at some point in their lives. It’s not just your allergy trigger that increases the risk. Having anaphylaxis once makes future allergic reactions of this type more likely.

Read on to discover:

  • How to recognize the signs and symptoms of anaphylaxis, as well as anaphylactic shock
  • What’s going on inside your body when you have an allergic reaction, whether it’s mild or severe like anaphylaxis
  • What to do in the event of an anaphylactic reaction, including the immediate treatment needed
  • Some of the common triggers and risk factors for this type of severe reaction

We will also look at a long-term treatment for some allergies that may lower the risk of anaphylaxis.

Signs and symptoms of anaphylaxis

An anaphylactic reaction tends to involve more than one part of your body, often but not always including skin allergy symptoms. It can also affect your airways, breathing and circulation. You may have any of these anaphylactic signs and symptoms and it could be different next time:

  • Widespread skin reactions, including hives and itching and flushed or pale skin
  • Low blood pressure (hypotension)
  • Constriction of your airways and a swollen tongue or throat, which may cause wheezing and trouble breathing
  • A weak and rapid pulse
  • Nausea, vomiting or diarrhea
  • Dizziness or fainting

Insect allergy made simple

Close-up of a wasp stinger which can cause more than an ouch if you’re allergic to the insect’s venom

Remembering these signs and recognizing them early can help minimize the severity of your anaphylactic reaction. If you’ve ever had anaphylaxis, did you feel as if something dreadful was about to happen? A sense of impending doom is another signal to use your emergency anaphylaxis medication and immediately seek emergency medical attention.

What is anaphylactic shock?

Shock is typically associated with a sudden drop in blood pressure (hypotension). There are various causes of shock and anaphylaxis is one of them. It’s because of chemicals like histamine your body releases as part of a severe systemic allergic reaction. When a person is in shock, their organs aren't getting enough blood or oxygen. If untreated, this can lead to permanent organ damage or even death.

Anaphylaxis can range from mild to severe. But the risk of anaphylactic shock is one reason to carry emergency medicine at all times (read more below) and consider wearing a medical alert bracelet.

How allergy and anaphylaxis work

Your immune system’s job is to defend your body against threats like bacteria, viruses, fungi and parasites. People with allergies have an overactive immune system which sounds the alarm when it doesn’t need to; for instance, when you breathe in pollen or eat a peanut. It makes immunoglobulin E (IgE) antibodies to watch out for that foreign substance and fight it off. You’re sensitized and could develop an allergy.

If you do, the IgE antibodies will spot the substance or allergen next time you meet it. They’ll trigger various cells to release chemicals like histamine to get rid of it from your body as fast as possible. This is an allergic reaction.

Child using a knife to scrape out a nearly empty peanut butter jar – a forbidden treat if they get peanut allergy symptoms

Tips to avoid peanut allergy

Anaphylaxis vs milder allergic reactions

The basic mechanism is the same for hay fever and anaphylaxis. Both involve IgE antibodies. Allergic reactions tend to start in mast cells at or near where you had contact with your trigger. There are mast cells in your skin and in the lining of your nose, airways, lungs and gut (mucosal tissue). Typically symptoms affect just that part of your body. The histamine could give you an itchy rash, runny nose or upset stomach.

Anaphylaxis also involves mast cells. But your immune system calls on other defences too. White blood cells called basophils release more histamine and chemicals like leukotrienes. This intensifies the allergic reaction, which can spread to your cardiovascular and respiratory systems, causing the systemic symptoms we’ve described.

How quickly does anaphylaxis start?

Anaphylaxis is a rapid onset allergic reaction. Symptoms usually start 5 to 30 minutes after you meet your trigger – although it could be up to an hour or two later.

Alpha gal syndrome is one exception. This is a rare allergy to lamb, pork, beef and venison that develops after a tick bite. It can cause anaphylaxis but the allergic reaction tends to start 4 to 8 hours after you’ve eaten.

Fast-acting treatment for anaphylaxis

The first and most important treatment for anaphylaxis is the hormone epinephrine. The exception may be if you’re already taking certain medications, for instance B-blockers or ACE-inhibitors, that could work against the epinephrine. Consult your healthcare provider about potential interactions with your current medication.

What is epinephrine?

The first and most important treatment for anaphylaxis is the hormone epinephrine. The exception may be if you’re already taking certain medications, for instance B-blockers or ACE-inhibitors, that could work against the epinephrine. Consult your healthcare provider about potential interactions with your current medication.

Epinephrine is a prescription medication that comes as an auto-injector for you to use in an emergency. Around 15-30% of anaphylactic reactions need more than one dose to ease the symptoms. So carry two at all times. And seek immediate medical attention or call 911, even if you feel better after using the auto-injector, in case of a delayed reaction.

How long does treatment go on for?

Biphasic anaphylaxis is when you get a second wave of symptoms some hours later. You need to be under medical observation in case that happens. It’s less common but symptoms can also drag on for several days. This is known as protracted anaphylaxis. In which case you might need to stay in hospital for longer.

What to do in the event of severe anaphylaxis

This step-by-step guide looks at how to help someone else who’s experiencing anaphylaxis. But you should also follow these tips if you have an anaphylactic reaction:

1. Use the auto-injector quickly to inject a dose of epinephrine. The instructions are usually on the side and it works through clothing.

2. Seek immediate medical attention or call 911 and ask for an ambulance. Say you think it’s anaphylaxis. Give the used auto-injector to the paramedics when they arrive so they know what medication the person has already had.

3. To help blood flow to the heart and maintain blood pressure lie the person down with their legs elevated. Do not do this if they’re pregnant, struggling to breathe or unconscious.

4. Wait 5 to 15 minutes. If the symptoms haven’t improved, and the ambulance hasn’t arrived yet to take them to the emergency room, use a second auto-injector.

Getting comfortable with anaphylaxis injections

Injecting yourself in the thigh may seem scary. But the needle of the auto-injector is smaller than a flu jab needle and your healthcare provider or pharmacist will show you how to do it. Practice with the training auto-injectors and involve your family in case you need their help. Is there a teacher at your child's school who knows how to give the injection? Ask the same question whenever they’re in someone else’s care.

Older children can carry and administer their own epinephrine. But they still need lots of support. Fatal allergic reactions to food are most common among adolescents and young adults. These are the risk-taking years when fitting in socially is also super important. One simple step could be finding them the right bag to carry the epinephrine, possibly insulated since it needs to be kept at room temperature.

Auto-injectors do expire. Always check the window to make sure it’s clear and not cloudy. And sign up to get a text or email alert from the company who makes yours when it’s time to replace them.

Common anaphylaxis triggers

Any allergy could cause anaphylaxis but it happens much more often with certain triggers. Children and teenagers are most at risk from food and insect stings. For adults, it’s medicine and insect stings.

  • Food: There are eight major allergens covered by food labeling laws. Of these chicken’s egg, cow’s milk, wheat and peanut are the most common causes of anaphylaxis in children. With adults it varies according to the diet where you live. These are some of the usual suspects: peanuts, tree nuts, seeds like sesame, wheat and shellfish. Also plant-based foods containing lipid transfer proteins (for instance, apples, grapes, peanuts, hazelnuts, almonds, walnuts, dried fruit and tomatoes).
  • Insect venom: Stings from fire ants, bees, wasps, yellow jackets or hornets.
  • Medicines: Most commonly, penicillin (and other antibiotics), muscle relaxants used in general anesthetics and insulin. Allergy immunotherapy can cause anaphylactic reactions too. Where that is a risk, treatment takes place under medical supervision.
  • Latex: Gloves (dental care can be a risk), medical devices and equipment, rubber bands, balloons and condoms.

It may only take a tiny amount of the trigger to cause anaphylaxis. But the risk does go up the greater your exposure.  

Labeled food containers in the refrigerator. Giving people with food allergies their own shelf helps avoid cross-contact

Food allergy: What
you need to know

Some other causes of anaphylaxis

It may not be IgE antibodies that trigger your mast cells and basophils. Blood and blood products used in transfusions can cause a different type of immune response. It can also trigger anaphylaxis.

Non-immunologic anaphylaxis is when the immune system isn’t thought to be involved. That covers severe reactions to aspirin and other non-steroid anti-inflammatory drugs (NSAIDs). Some opioids and chemotherapy drugs can also cause anaphylaxis. So can contrast agents, substances you might be given before an MRI scan and other medical imaging exams. And some sulphites used to preserve food.

In some cases there is no obvious trigger. That’s idiopathic anaphylaxis. In others the reaction may only happen in specific circumstances, for instance when exercise is combined with your trigger.

Anaphylaxis: When it takes more than one trigger

It’s rare but physical activity can cause anaphylaxis. This might be the only trigger or what’s known as a co-factor with something else. For instance, you may be allergic to a food like wheat or shellfish but have no symptoms unless you exercise a few hours before or after eating it. The condition is called food-dependent exercise-induced anaphylaxis (FDEIA) and it’s more common in women under 30 years old. Aspirin and other NSAIDs can also cause life-threatening reactions taken shortly before or after exercise.

Other factors can activate food allergy. These include extreme cold, stress, drinking alcohol with food or premenstrual hormone changes.

Can you predict who will get anaphylaxis?

There’s no way to know for certain who will have an anaphylactic reaction. But a component blood test may help your healthcare provider or allergist assess your risk level. In allergy, your immune system reacts to proteins. Some peanut, some tree nut and insect venom proteins are more likely to trigger anaphylaxis. This type of test can show if you’re sensitized to them.

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Do you think you may have had anaphylaxis or be at risk of this type of severe allergic reaction? We can help you find an allergy specialist nearby

Other risk factors to consider include:

  • a family history of anaphylactic reactions
  • having already had anaphylaxis
  • having other cardiovascular or respiratory medical conditions, especially if they’re poorly controlled
  • mastocytosis, a rare condition when your body makes too many mast cells

Your healthcare provider will ask for a detailed medical history, not only for you but for your family too.

Is there a cure for anaphylaxis?

There’s no treatment yet that can prevent or cure anaphylaxis. For certain allergies immunotherapy is used to train the immune system not to react as strongly. The idea is to reduce your sensitivity over several years with regular tiny doses of the allergen. The treatment is available for peanut and for hymenoptera (bee and wasp) venom. Immunotherapy is not suitable for everyone and you would still have to avoid allergens. Your healthcare provider or allergist can tell you more.

Desensitization tends to be a short-term solution to a drug allergy. That is, when there’s no alternative to a particular antibiotic, perhaps, or chemotherapy. It generally happens in hospital. The dose builds up slowly until you can take the minimum necessary with few side effects. Should you stop taking the drug every day, then need it again, you’d have to repeat the process.


Anaphylaxis is a life-threatening allergic reaction affecting your whole body. It needs immediate treatment with epinephrine.

The severity of anaphylactic reactions can be minimized by recognizing the symptoms early, having the proper medication available for self-treatment and seeking emergency medical care promptly.

Common causes include food, insect venom, medicine and latex allergies. A detailed blood test can help assess if you’re at risk, alongside your medical history and your family’s. Allergy immunotherapy may reduce that risk.

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Last medically reviewed on 08/11/2022