Anaphylaxis is a serious allergic reaction that is rapid in onset and may cause death. It typically causes more than one of the following: an itchy rash, throat or tongue swelling, shortness of breath, vomiting, lightheadedness, and low blood pressure. These symptoms typically come on over minutes to hours.
Common causes include insect bites and stings, foods, and medications. Other causes include latex exposure and exercise. Additionally cases may occur without an obvious reason. The mechanism involves the release of mediators from certain types of white blood cells triggered by either immunologic or non-immunologic mechanisms. Diagnosis is based on the presenting symptoms and signs after exposure to a potential allergen.
The primary treatment of anaphylaxis is epinephrine injection into a muscle, intravenous fluids, and positioning the person flat. Additional doses of epinephrine may be required. Other measures, such as antihistamines and steroids, are complementary. Carrying an epinephrine autoinjector and identification regarding the condition is recommended in people with a history of anaphylaxis.
Worldwide, 0.05–2% of the population is estimated to experience anaphylaxis at some point in life. Rates appear to be increasing. It occurs most often in young people and females. Of people who go to a hospital with anaphylaxis in the United States about 0.3% die. The term comes from the Ancient Greek: ἀνά ana “against”, and the Ancient Greek: φύλαξις phylaxis “protection”.
Your immune system produces antibodies that defend against foreign substances. This is good when a foreign substance is harmful, such as certain bacteria or viruses. But some people’s immune systems overreact to substances that don’t normally cause an allergic reaction.
Allergy symptoms aren’t usually life-threatening, but a severe allergic reaction can lead to anaphylaxis. Even if you or your child has had only a mild anaphylactic reaction in the past, there’s a risk of more severe anaphylaxis after another exposure to the allergy-causing substance.
The most common anaphylaxis triggers in children are food allergies, such as to peanuts, and tree nuts, fish, shellfish and milk. Besides allergy to peanuts, nuts, fish and shellfish, anaphylaxis triggers in adults include:
- Certain medications, including antibiotics, aspirin and other over-the-counter pain relievers, and the intravenous (IV) contrast used in some imaging tests
- Stings from bees, yellow jackets, wasps, hornets and fire ants
Although not common, some people develop anaphylaxis from aerobic exercise, such as jogging, or even less intense physical activity, such as walking. Eating certain foods before exercise or exercising when the weather is hot, cold or humid also has been linked to anaphylaxis in some people. Talk with your doctor about precautions to take when exercising.
If you don’t know what triggers your allergy attack, certain tests can help identify the allergen. In some cases, the cause of anaphylaxis is never identified (idiopathic anaphylaxis).
There aren’t many known risk factors for anaphylaxis, but some things that might increase your risk include:
- Previous anaphylaxis. If you’ve had anaphylaxis once, your risk of having this serious reaction increases. Future reactions might be more severe than the first reaction.
- Allergies or asthma. People who have either condition are at increased risk of having anaphylaxis.
- Certain other conditions. These include heart disease and an abnormal accumulation of a certain type of white blood cell (mastocytosis).
Anaphylaxis symptoms usually occur within minutes of exposure to an allergen. Sometimes, however, it can occur a half-hour or longer after exposure. Signs and symptoms include:
- 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 can cause wheezing and trouble breathing
- A weak and rapid pulse
- Nausea, vomiting or diarrhea
- Dizziness or fainting
Your doctor will ask you questions about previous allergic reactions, including whether you’ve reacted to:
- Particular foods
- Insect stings
To help confirm the diagnosis:
- You might be given a blood test to measure the amount of a certain enzyme (tryptase) that can be elevated up to three hours after anaphylaxis
- You might be tested for allergies with skin tests or blood tests to help determine your trigger
Many conditions have signs and symptoms similar to those of anaphylaxis. Your doctor will want to rule out other conditions.
During an anaphylactic attack, you might receive cardiopulmonary resuscitation (CPR) if you stop breathing or your heart stops beating. You might also be given medications, including:
- Epinephrine (adrenaline) to reduce your body’s allergic response
- Oxygen, to help you breathe
- Intravenous (IV) antihistamines and cortisone to reduce inflammation of your air passages and improve breathing
- A beta-agonist (such as albuterol) to relieve breathing symptoms
What to do in an emergency
If you’re with someone who’s having an allergic reaction and shows signs of shock, act fast. Look for pale, cool and clammy skin; a weak, rapid pulse; trouble breathing; confusion; and loss of consciousness. Do the following immediately:
- Call 911 or emergency medical help.
- Use an epinephrine autoinjector, if available, by pressing it into the person’s thigh.
- Make sure the person is lying down and elevate his or her legs.
- Check the person’s pulse and breathing and, if necessary, administer CPR or other first-aid measures.
Using an autoinjector
Many people at risk of anaphylaxis carry an autoinjector. This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against the thigh. Always replace epinephrine before its expiration date, or it might not work properly.
Using an autoinjector immediately can keep anaphylaxis from worsening and could save your life. Be sure you know how to use the autoinjector. Also, make sure the people closest to you know how to use it.
If insect stings trigger your anaphylactic reaction, a series of allergy shots (immunotherapy) might reduce your body’s allergic response and prevent a severe reaction in the future.
Unfortunately, in most other cases there’s no way to treat the underlying immune system condition that can lead to anaphylaxis. But you can take steps to prevent a future attack — and be prepared if one occurs.
- Try to avoid your allergy triggers.
- Carry self-administered epinephrine. During an anaphylactic attack, you can give yourself the drug using an autoinjector (EpiPen, others).
The best way to prevent anaphylaxis is to avoid substances that cause this severe reaction. Also:
- Wear a medical alert necklace or bracelet to indicate you have an allergy to specific drugs or other substances.
- Keep an emergency kit with prescribed medications available at all times. Your doctor can advise you on the contents. If you have an epinephrine autoinjector, check the expiration date and be sure to refill your prescription before it expires.
- Be sure to alert all your doctors to medication reactions you’ve had.
- If you’re allergic to stinging insects, use caution around them. Wear long-sleeved shirts and pants; don’t walk barefoot on grass; avoid bright colors; don’t wear perfumes, colognes or scented lotions; and don’t drink from open soda cans outdoors. Stay calm when near a stinging insect. Move away slowly and avoid slapping at the insect.
- If you have food allergies, carefully read the labels of all the foods you buy and eat. Manufacturing processes can change, so it’s important to periodically recheck the labels of foods you commonly eat.
When eating out, ask how each dish is prepared, and find out what ingredients it contains. Even small amounts of food you’re allergic to can cause a serious reaction.
Having a potentially life-threatening reaction is frightening, whether it happens to you, others close to you or your child. Developing an anaphylaxis emergency action plan can help put your mind at ease.
Work with your own or your child’s doctor to develop this written, step-by-step plan of what to do in the event of a reaction. Then share your plan with teachers, baby sitters and other caregivers.
If your child has a severe allergy or has had anaphylaxis, talk to the school nurse and teachers to find out what plans they have for dealing with an emergency. Make sure school officials have a current autoinjector.
Fatal anaphylaxis is infrequent but not rare; milder forms occur much more frequently. Up to 500-1000 fatal cases of anaphylaxis per year are estimated to occur in the United States. Estimated mortality rates range from 0.65-2% of patients with anaphylaxis.
Reactions to foods are thought to be the most common cause of anaphylaxis when it occurs outside of the hospital and are estimated to cause 125 deaths per year in the United States. Severe reactions to penicillin occur with a frequency of 1-5 cases per 10,000 patient courses, with fatalities in 1 case per 50,000-100,000 courses. Fewer than 100 fatal reactions to Hymenoptera stings are reported each year in the United States, but this is considered to be an underestimate.
Anaphylaxis to conventional radiocontrast media (RCM) was estimated to have caused up to 900 fatalities in 1975, or 0.009% of patients receiving RCM.In one series, the reported risk of adverse reactions (mild or severe) in patients receiving lower osmolar RCM agents is 3.13% compared with 12.66% for patients receiving conventional RCM.The study also reported premedication did not lower the risk of nonionic reactions further. The rate of fatal anaphylaxis is also reduced significantly by lower-osmolar RCM, approximately 1 in 168,000 administrations.
In the United Kingdom, half of fatal anaphylaxis episodes are of iatrogenic origin (eg, anesthesia, antibiotics, radiocontrast media), while foods and insect stings each account for a quarter of the fatal episodes.
The most common causes of death are cardiovascular collapse and respiratory compromise. One report examined 214 anaphylactic fatalities for which the mode of death could be surmised in 196, 98 of which were due to asphyxia (49 lower airways [bronchospasm], 26 both upper and lower airways, and 23 upper airways [angioedema]). The fatalities from acute bronchospasm occurred almost exclusively in those with preexisting asthma.
Another analysis of 23 unselected cases of fatal anaphylaxis determined that 16 of 20 “immediate” deaths (death occurring within one hour of symptom onset) and 16 of the 23 cases that underwent autopsy were due to upper airway edema.
Death can occur rapidly. An analysis of anaphylaxis fatalities occurring in the United Kingdom from 1992 to 2001 revealed the interval between initial onset of food anaphylaxis symptoms and fatal cardiopulmonary arrest averaged 25-35 minutes, which was longer than for drugs (mean, 10-20 minutes pre-hospital; 5 minutes in-hospital) or for insect stings (10-15 minutes).
Asthma is a risk factor for fatal anaphylaxis. Delayed administration of epinephrine is also a risk factor for fatal outcomes.
Posture also influences anaphylaxis outcomes. In a retrospective review of prehospital anaphylactic fatalities in the United Kingdom, the postural history was known for 10 individuals. Four of the 10 fatalities were associated with the assumption of an upright or sitting posture during anaphylaxis. Postmortem findings were consistent with pulseless electrical activity and an “empty heart” attributed to reduced venous return from vasodilation and redistribution of intravascular volume from the central to the peripheral compartment.
Patients may experience multiple anaphylactic episodes. The Rochester study detected a total of 154 anaphylactic episodes involving 133 people in a 5-year period. Most patients (116) had only 1 episode in those 5 years. Thirteen people had 2 episodes, and 4 people had 3 episodes.
In contrast, in the Memphis study, 48% of patients had 3 or more anaphylactic episodes. Of the 112 patients who responded to survey, however, 38 patients (34%) reported a recurrence of symptoms and the remaining 74 patients (66%) reported remission of symptoms. Overall, 85% of patients either were in remission or reported diminished symptom severity in a subsequent episode or episodes. The Memphis study evaluated a referral population and also deliberately excluded patients with anaphylaxis due to insect stings or SCIT.
Some people may go into anaphylactic shock. It’s also possible to stop breathing or experience airway blockage due to the inflammation of the airways. Sometimes, it can cause a heart attack. All of these complications are potentially fatal.