What Is Anaphylaxis? Symptoms, Causes, Diagnosis, Treatment, and Prevention
Anaphylaxis is a serious allergic reaction that typically affects more than one area of your body at once.
It can be triggered by exposure to any allergen — a substance that you’ve become allergic to. The most common triggers are foods, medications, insect venom, and latex.
Anaphylaxis requires immediate treatment with an epinephrine injection. This is usually administered before the person gets to a hospital emergency room, which is where they should go as soon as possible.
If you know that you’re prone to an anaphylactic reaction, you should carry an epinephrine self-injection device with you at all times. You should also avoid known triggers of anaphylaxis.
Because anaphylaxis involves different parts of the immune system, medical researchers are still working to understand why it may affect areas such as your skin, lungs, digestive tract, or even your heart and blood pressure.
In an anaphylactic reaction, your immune system releases a number of chemicals to fight off what it perceives as a dangerous substance invading your body. These immune system chemicals can have different effects on different areas of your body.
One chemical implicated in anaphylaxis is histamine, which is the target of antihistamine drugs. Histamine is one player in the process that relaxes your blood vessels, tightens your throat and airways, and increases mucus production.
Since histamine is only one of numerous chemicals involved in an anaphylactic reaction, taking an antihistamine alone tends to have limited benefits. An epinephrine injection is considered the only effective treatment for anaphylaxis.
If it’s severe enough and left untreated, anaphylaxis can cause you to go into shock. Signs of shock often include rapid breathing, pale or clammy skin, dizziness, and a rapid, weak pulse.
An allergic reaction happens when your immune system overreacts to a substance it believes to be a threat, otherwise known as an allergen.
In response to an allergen, your immune system releases chemicals that cause allergy symptoms. These symptoms typically occur in one location of your body for a given allergen.
But in some cases, your immune system releases a wide range of chemicals, and in greater quantities than usual, causing reactions in multiple areas of your body. Collectively, these reactions are known as anaphylaxis.
It’s not fully understood why allergic reactions happen with certain substances in some people and not in others. Genetics is likely involved in some of these differences.
Once your body is sensitized to an allergen, an allergic reaction of any magnitude can occur.
An anaphylactic reaction tends to affect multiple areas of your body at once — not just your skin or upper respiratory tract, the way a typical allergic reaction does.
Unease or anxiousness (often described as a “feeling of impending doom”)
Flushed or pale skin
Swollen throat and hoarse voice
Swelling of the face and tongue
Chest tightness
Nasal congestion
Nausea or vomiting
Weak or rapid pulse
Dizziness
Heart palpitations
Loss of consciousness
In severe cases, anaphylaxis can cause a person to stop breathing or to go into shock — an acute condition that leads to a drop in blood pressure to dangerously low levels. Under these circumstances, anaphylaxis can be fatal unless emergency help is immediately available.
Anaphylaxis symptoms usually begin within a few minutes after you come into contact with the allergen that causes it, although in some cases it can take 30 minutes or longer for anaphylaxis to develop.
Generally speaking, your risk for anaphylaxis is higher if you’ve previously had a severe allergic reaction, including anaphylaxis.
Most people have heard that peanuts can cause anaphylaxis if you’re allergic to them, but did you know that some women experience anaphylaxis during a certain phase of their menstrual cycle? Or that a bite from a lone star tick can lead to an allergy to red meat?
Many seemingly weird things can bring on anaphylaxis in people who are susceptible to it, and in some cases it can be difficult to figure out what’s causing it.
If you’re experiencing symptoms of anaphylaxis but aren’t sure what’s causing it, see an allergist for help.
To figure out if your symptoms are caused by an allergic reaction or anaphylaxis, your doctor may ask you questions about your previous reactions to foods, medications, insect bites or stings, and latex.
To help confirm a diagnosis of anaphylaxis, your doctor may order the following tests:
Blood test for tryptase (an enzyme that may be elevated for up to three hours after anaphylaxis)
Skin or blood tests for specific allergies
The primary treatment for anaphylaxis is epinephrine, usually delivered with an auto-injector, which is available by prescription.
In August 2024, an epinephrine nasal spray (Neffy) was approved in the United States as an alternative to injections for people with a history of severe allergic reactions. While this form of epinephrine may be easier for some people to use, it may also be less effective in people with certain nasal conditions, like nasal polyps.
Epinephrine reverses the symptoms of anaphylaxis in several ways:
It causes the blood vessels to constrict, reducing swelling and raising blood pressure.
It relaxes the muscles of the airways, making it easier to breathe.
It slows or stops the release of some of the chemicals produced in an allergic reaction.
People who are at risk for anaphylaxis should carry an epinephrine auto-injector or nasal spray with them at all times and familiarize themselves with the instructions for using it.
Epinephrine should be injected into the side of the thigh muscle for rapid absorption. It can be injected through clothing, if necessary.
Sometimes a second dose of epinephrine is needed, if anaphylaxis symptoms recur. If this is necessary, a new auto-injector should be used.
Once a dose of epinephrine has been injected, the person experiencing anaphylaxis should be taken to the nearest emergency department for further treatment.
To help prevent shock (a sudden drop in blood pressure) during an anaphylactic reaction, after receiving epinephrine, the person should lie flat on their back with their feet elevated about 12 inches (30 centimeters) and covered by a coat or blanket. This should only be done if it feels comfortable for the person and if no injuries are suspected.
Antihistamines and corticosteroids are given intravenously (by IV) to reduce inflammation in your airways and help you breathe.
Beta-agonists also can help open up your airways and may be given either by IV or in an inhaled form.
You may also be given fluids by IV to increase your blood volume and blood pressure, or given oxygen through a tube to help you breathe.
Without prompt treatment, anaphylaxis can be life-threatening. It’s essential to seek emergency treatment to minimize the risk of death.
If you receive prompt treatment for anaphylaxis — such as an epinephrine injection, followed by emergency medical care — symptoms usually get better, often without any lasting effects.
Symptoms of anaphylaxis often develop within a few seconds or minutes after exposure to an allergen, but can take 30 minutes or longer to develop in rare cases.
An anaphylactic reaction can get worse quickly once it starts, to the point where you collapse, stop breathing, lose consciousness, or have seizures within one to two minutes of its onset — although it may take longer to fully worsen. If treatment isn’t given rapidly, such a reaction can be fatal.
Sometimes symptoms of anaphylaxis return several hours after the initial exposure to an allergen, or even later (known as biphasic anaphylaxis). This second reaction tends to be milder than the first one, but in some cases it may be more severe or even fatal.
Some people have what’s known as protracted anaphylaxis, in which symptoms last for several hours or longer. This possibility is one reason it’s important to be monitored in an emergency medical setting, even if your symptoms are initially resolved by an epinephrine injection.
When it comes to anaphylaxis, the best treatment is to prevent the reaction in the first place. This means identifying what you’re allergic to and finding ways to avoid those allergens.
For people with food allergies, that means being sure to:
Read all food package labels carefully to look for allergens.
Avoid buying food from bulk bins, which might be cross-contaminated.
Communicate your food needs at restaurants.
Make sure family members and friends know about your food allergy.
For people with insect venom allergies, you should:
Know where you’re likely to encounter the insects you’re allergic to.
Cover up with clothes and shoes when you go outdoors, and avoid wearing bright colors, such as yellows and reds.
Avoid drinking from open beverage cans or bottles while outside.
Learn how to respond if you encounter a biting or stinging insect.
If you’re allergic to drugs, take these steps:
Let all your healthcare providers, including your dentist, know about your drug allergy.
Wear or carry a medical ID that lists your drug allergy or allergies.
If you don’t receive prompt treatment, anaphylaxis can lead to a number of potentially life-threatening complications, including:
Blocked or closed airway
Cardiac arrest (no heartbeat)
Respiratory arrest (no breathing)
Shock (sudden drop in blood pressure)
Depending on how quickly you receive emergency medical attention, it may be possible to be revived if you experience these complications.
While estimates vary, the lifetime risk for anaphylaxis in the United States is believed to be between 0.05 and 2 percent.
Worldwide, between 0.5 and 1 percent of hospitalizations for anaphylaxis result in death. Food allergies are less likely than other allergy types to cause a fatal reaction. The fatality rate for anaphylaxis hospitalizations has gone down over recent decades in the United States, the United Kingdom, and Australia — which may reflect better recognition and faster treatment of anaphylaxis in these countries.
Among the estimated 33 million Americans with food allergies, about 1 in 13 children and 1 in 10 adults are reported to have experienced a severe reaction. Between 2007 and 2016, the reported incidence of anaphylaxis due to food allergies increased by 377 percent, for reasons that aren’t completely clear.
There’s some evidence that Black and Hispanic Americans are at higher risk for food allergies that may lead to anaphylaxis than white or Asian Americans, as well as anaphylaxis itself.
One study found that the overall rate of food allergies was 6.5 percent for Asian Americans, 7.0 percent for white Americans, 8.4 percent for Hispanic Americans, and 8.9 percent for Black Americans. Among those with food allergies, the proportion that reported using an epinephrine auto-injector at least once was 20.9 percent for white participants, 22.6 percent for Asian participants, 23.6 percent for Black participants, and 24.6 percent for Hispanic participants.
The proportion of participants that reported an emergency room visit for food allergies in the last year was 8.3 percent for white Americans, 9.9 percent for Asian Americans, 13.5 percent for Black Americans, and 15.5 percent for Hispanic Americans. A higher number of lifetime emergency room visits was also seen among Black and Hispanic participants.
In the United States, childhood food allergies have increased at a faster rate in Black and Hispanic children — 2.1 percent per decade for Black children and 1.2 percent per decade for Hispanic children — than the 1 percent per decade seen in white children.
Regardless of your race or ethnicity, you should see a doctor if you or your child shows any signs of even a mild allergic reaction to food, insect bites, or medications (such as a rash or hives). Call for emergency services at the first sign of a severe allergic reaction.
Anaphylaxis can be caused by different kinds of allergies, including:
Food allergies
Drug allergies
Insect venom allergies
Latex allergy
In addition, untreated anaphylaxis can lead to serious or life-threatening health conditions, such as:
Anaphylaxis is a severe type of allergic reaction, involving multiple areas of your body, that requires immediate treatment with epinephrine. The best way to avoid the risk of serious complications, like shock or cardiac arrest, is to avoid the substance you’re allergic to.
