Anaphylaxis is a serious allergic reaction. It begins suddenly and may cause death. Anaphylaxis has many symptoms, such as an itchy rash, throat swelling, breathing problems, and low blood pressure. Common causes include insect bites, foods, and medications.
Anaphylaxis happens when a person eats, breathes in, or is injected with an allergen (something they are allergic to). Their immune system over-reacts. It sends out special proteins from inside certain white blood cells. These proteins can start an allergic reaction or make the reaction worse.
Anaphylaxis is diagnosed from a person’s signs and symptoms. The best treatment is an injection (a shot) of epinephrine (adrenaline). Sometimes doctors give other medicines along with epinephrine.
Worldwide, about 0.05–2% of people have anaphylaxis at some point in their lives. Anaphylaxis appears to be getting more common.
Cases of anaphylaxis have been reported since ancient times.
The condition was originally named "aphylaxis" by Charles Richet in 1902. In 1913, Richet was awarded the Nobel Prize in Medicine and Physiology for his work on anaphylaxis.
Later, the name was changed to "anaphylaxis" because it sounded nicer. The word "anaphylaxis" comes from the Greek words ἀνά (ana), "against", and φύλαξις (phyla's), "protection."
Anaphylaxis can cause many different signs and symptoms over minutes or hours. If the anaphylaxis is caused by something that entered the body directly through the bloodstream (through a vein), symptoms appear within an average of 5 to 30 minutes. If it is caused by a food the person ate, symptoms appear within an average of 2 hours.
The most common body systems affected by anaphylaxis include:
People with anaphylaxis usually have problems with two or more of these body systems.
Skin symptoms usually include:
In 20% of cases, the tongue or throat may swell up, which can cause breathing problems. If a person is having breathing problems, the skin may turn blue because the body is not getting enough oxygen. This is called cyanosis.
Respiratory signs and symptoms include:
When a person has anaphylaxis, some of the cells in the heart may release histamine. This can cause the heart’s blood vessels to get narrower suddenly (this is called "coronary artery spasm"). If the heart's blood vessels get too narrow, the heart cannot get enough blood. This can cause many serious problems:
Anaphylaxis can also cause low blood pressure. This may be caused by distributive shock, where the body's blood vessels get much wider because of the chemicals released by the immune system. It can also be caused by cardiogenic shock, where the heart is not getting enough blood to pump out to the rest of the body.
Low blood pressure can cause many problems, including:
In rare cases, very low blood pressure may be the only sign of anaphylaxis.
People who already have heart disease are at greater risk of having heart problems from anaphylaxis.
Anaphylaxis can also cause problems with other body systems:
Anaphylaxis can be caused by the body’s response to almost any foreign substance (anything that is outside the body). Common causes include venom from insect bites or stings; foods; and medications. In children and young adults, foods are the most common trigger (or cause) of anaphylaxis. In older adults, medications and insect bites or stings are more common triggers.
Many foods can trigger anaphylaxis, even when the food is eaten for the first time. In the Western world, the most common causes are eating or touching peanuts, wheat, tree nuts, shellfish, milk, and eggs. In the Middle East, sesame is a common trigger food. In Asia, rice and chickpeas often cause anaphylaxis.
Severe cases of anaphylaxis usually happen when a person eats the trigger food. However, some people have severe anaphylaxis when the trigger food touches some part of their body.
Children can outgrow their allergies. For example, by age 16:
Any medication may cause anaphylaxis. The most common are β-lactam antibiotics (such as penicillin), then aspirin and NSAIDs.
Venom from stinging or biting insects, like bees and wasps (Hymenoptera) or kissing bugs (Triatominae), may cause anaphylaxis. If a person has a bad allergic reaction to venom once, they have a greater risk of having anaphylaxis if they are stung or bitten again. However, half of the people who die of anaphylaxis have had no anaphylactic reaction before.
Certain diseases, called atopic diseases, can make a person more likely to have allergies. Atopic diseases include asthma, eczema, and allergic rhinitis. People with these diseases have a high risk of anaphylaxis from food, latex, and radiocontrast agents. However, these people do not have a higher risk from injected medications or stings.
One study of children with anaphylaxis found that 60% had a history of previous atopic diseases. More than 90% of children who die from anaphylaxis have asthma.
The risk of having another anaphylactic reaction decreases as a person avoids the trigger for longer and longer.
Anaphylaxis usually happens because the immune system over-reacts to an allergen. The immune system releases mast cells and basophils, which are types of white blood cells. The immune system sees the trigger as something bad and sends out white blood cells to kill it. The mast cells and basophils attach to the allergen to try to kill it. However, because the system is over-reacting, the mast cells and basophils explode and dump out chemicals that cause inflammation, like histamine. Histamine causes many of the symptoms of anaphylaxis. For example:
Anaphylaxis is diagnosed based on signs, symptoms, and knowing that a person has been exposed to an allergen. It is very likely that a person has anaphylaxis if any of these three things happen within minutes or hours after they were exposed to an allergen:
If a person has a bad reaction to an insect sting or a medication, blood tests for tryptase or histamine might be useful in diagnosing anaphylaxis. However, these tests are not very useful if the cause is food, or if the person has a normal blood pressure. Also, these tests cannot say for sure that a person does not have anaphylaxis.
Allergy testing may help to identify what caused a person’s anaphylaxis. Skin allergy tests (such as patch tests) can be done for certain foods and venoms. Skin tests can diagnose an allergy to penicillin, but there are no skin tests for other medications. Blood tests can diagnose milk, egg, peanut, tree nut and fish allergies.
Sometimes it is difficult to tell the difference between anaphylaxis; asthma; fainting caused by not having enough oxygen; and panic attacks. However, there are some important differences between these conditions:
The best way to prevent anaphylaxis is to avoid the trigger that caused anaphylaxis in the past. When this is not possible, there may be treatments to make the body stop reacting to the trigger. This is called desensitization. For example, treatment of the immune system (immunotherapy) with Hymenoptera venoms is able to make 80–90% of adults and 98% of children stop having allergic reactions to bees, wasps, hornets, yellow jackets, and fire ants. Most people who are allergic to certain medicines can just avoid those medicines. However, desensitization is possible for many medications (for example, many chemotherapies) if the person has to take those medicines.
People with latex allergies may have to avoid "cross-reactive foods." These are foods that have ingredients that are similar to latex. Examples of these foods includeavocados, bananas, and potatoes.
Anaphylaxis is a medical emergency that may require emergency medical treatment. Some patients need help keeping their airways open so they can breathe in air. Other patients need to be given extra oxygen or large amounts of intravenous fluids (fluids given through a needle into a vein).