Anaphylaxis is a rare but severe allergic reaction that can affect the skin, lungs, nose, throat, gastrointestinal tract and heart. Roughly 30 out of 100,000 people will experience anaphylaxis. It is a systemic (involving more than one body system) allergic reaction that occurs after a person has been sensitized to a particular allergen, and subsequently encounters that allergen at a later time.
Because anaphylaxis is an allergic reaction, a person usually does not experience an attack the first time they encounter the allergen.
An initial encounter creates the opportunity for sensitization, in which the immune system mistakenly recognizes the allergen as a harmful substance and creates immunoglobulin E (IgE) antibodies.
These antibodies trigger the allergic reaction the next time the individual encounters the allergen. Frequently, an individual is unaware of the sensitization process as it is taking place and may not remember having been exposed to the allergen prior to an episode of anaphylaxis.
During an allergic reaction, the body recognizes the allergen as an antigen, or foreign invader. IgE antibodies that had been created during sensitization, and had attached themselves to cells in the body called mast cells and basophils, now go into action. When IgE comes into contact with the antigen, it signals the cells to which it is attached to release chemical mediators such as histamine.
These chemical mediators cause inflammation, a protective response of the immune system designed to help drive the antigen out of the body. In addition, the chemicals trigger other responses in the tissues that lead to other symptoms of an allergic reaction.
In a typical allergic reaction, only certain cells in a section of the body react. In anaphylaxis, two or more body systems undergo an allergic reaction. As the tissues of the body release histamine and other substances, the airways constrict. Blood vessels dilate, lowering blood pressure severely and causing lightheadedness. Fluid leaks from the bloodstream into the tissues, resulting in lower blood volume. Bronchial tissues swell, causing breathing difficulties.
These changes lead to anaphylactic shock. As blood pressure plummets, the heart stops pumping blood to the tissues, a condition known as cardiovascular collapse. Tissues and organs fail to get the fluids and oxygen they need to survive. Sometimes fluid leaks into the alveoli (air sacs) of the lungs, causing pulmonary edema (fluid and swelling in the lungs).
An immediate epinephrine injection is necessary to reverse these symptoms. Without it, anaphylactic shock can be fatal. Anyone who suspects they are having an anaphylactic reaction should take epinephrine immediately and call an ambulance for additional medical attention.
There are five primary types of triggers for anaphylaxis:
About 50 percent of anaphylactic attacks are idiopathic, in which a trigger cannot be identified. Sometimes, a trigger will become evident after subsequent anaphylactic episodes.
Although anaphylaxis is not a common condition, those with asthma as well as allergies may be at increased risk for having an anaphylactic reaction. In addition, patients who have had prior reactions are at increased risk for subsequent anaphylactic reactions.
Related conditions for anaphylaxis
Occasionally, an individual will suffer symptoms that mimic those of anaphylaxis, but which have not been caused by allergies. This is called an anaphylactoid reaction, and it occurs even though there was no previous exposure or sensitization to an allergen. Immunoglobulin E (IgE) antibodies are not involved in this condition. Instead, mast cells and basophils are directly stimulated to react without IgE stimulation.
A typical example of anaphylactoid reaction occurs when an individual shows symptoms after receiving radiographic contrast material, the dye injected into the arteries and veins before an x-ray procedure. Other drugs known to trigger an anaphylactoid reaction include polymyxin (an antibiotic) and morphine (a painkiller).
Anaphylactoid reactions respond well to the same treatment used for treating anaphylaxis. A person should immediately take epinephrine regardless of whether they believe they are having an anaphylactic or anaphylactoid reaction.
Potential causes of anaphylaxis
Anaphylaxis is caused by an extreme immune system reaction. Allergens that trigger anaphylaxis can be introduced to the body in several ways, including:
Frequently, anaphylaxis is the result of an injection of the allergen under a person’s skin. This includes:
Bee, hornet, wasp, yellow jacket, fire ant and other insect stings.
Syringe-and-needle injections of some vaccines (particularly those made with horse serum).
Blood transfusions (not really anaphylactic, but anaphylactoid, which does not involve an allergen or IgE).
Allergens injected into a patient during allergy skin testing or allergy shots (immunotherapy).
Medications, including those used in treatments (e.g., antibiotics) and in testing (e.g., contrast dyes). These reactions may be anaphylactic or anaphylactoid.
The two most common allergies associated with ingesting allergens are drug allergies and food allergies. While people can be allergic to nearly any type of drug, those most commonly associated with anaphylaxis include:
Antibiotics, especially penicillin and related drugs (usually and anaphylactic reaction)
Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (usually an anaphylactoid reaction)
Prescription opiate pain medications, such as codeine (usually an anaphylactoid reaction)
Even small bites of certain foods can trigger anaphylaxis in extremely allergic individuals. In very few cases, mere skin contact with the food can cause problems. Foods known to trigger anaphylaxis include:
Seafood (including fish and shellfish)
Tree nuts (e.g., almond, walnut, hazel, cashew)
Eggs (particularly in children)
Cow’s milk (particularly in children)
Additives, including food coloring and preservatives (usually an anaphylactoid reaction)
Though rare, inhalation can trigger anaphylaxis. For example, those with latex allergies could be in danger after inhaling particles from rubber gloves. Healthcare workers are at particular risk because they are exposed to latex more frequently than the general public. Those with urinary tract abnormalities, children with spina bifida (a birth defect in which part of one or more vertebrae fails to fully develop) and people who have had multiple surgical procedures are also at higher risk for latex allergies.
Medications may also cause reactions by inhalation. Parents, patients or pharmacists preparing medications are most susceptible.
Sometimes a combination of factors is necessary to trigger anaphylaxis. For example, some individuals must be exposed to two or more allergens before they react. In other cases, a combination of allergen exposure and subsequent exercise is to blame for an individual’s anaphylaxis.
Physicians are not always able to determine the cause of an anaphylactic reaction. Cases in which a trigger cannot be identified are labeled idiopathic.
Signs and symptoms of anaphylaxis
Symptoms of anaphylaxis generally occur immediately after exposure to the allergen to which the person is sensitive. However, it can take as long as several hours after exposure before signs of anaphylaxis appear. The more rapidly symptoms appear, the more severe they are likely to become.
Symptoms of an anaphylactic reaction can affect many different parts of the body. Early signs and symptoms include:
Shortness of breath
Choking or difficulty breathing
Chest pain or tightness
Hives (including on the lips, eyelids, throat and tongue)
Bluish tint to skin (cyanosis), including lips or nail beds
Severe itching of the eyes, mouth or throat
Palpitations (an awareness of a strong, fast, irregular, abnormal or “galloping” heartbeat)
Inability to swallow
Swelling of the throat or tongue
Tightness in the throat
Rapid or weak pulse
Low blood pressure
Most cases of anaphylaxis involve cardiovascular and/or respiratory symptoms. The pattern of symptoms also typically remains the same for an individual from episode to episode. However, subsequent reactions can be more severe than the first. Without immediate emergency treatment, anaphylaxis can quickly progress to anaphylactic shock and become deadly.
More advanced symptoms include:
Collapse or loss of consciousness
Loss of bladder control
Those who experience an anaphylactic reaction are in life-threatening danger and need immediate medical attention. Individuals should use epinephrine at the first sign of an anaphylactic reaction and then call an ambulance for additional medical treatment. For more information, see Treatment options.
Diagnosis methods for anaphylaxis
Anaphylaxis is a condition that cannot be diagnosed ahead of time. It becomes apparent only after an individual has suffered an allergic reaction, and is diagnosed solely on the basis of the symptoms experienced and their severity.
However, a physician may recommend allergy skin testing to determine the risks to an individual of exposure to certain allergens. For example, a physician treating an individual who has experienced anaphylaxis in reaction to penicillin may use a skin test to try out alternative antibiotics. Such testing must be done with great care, as there is a chance the procedure could provoke anaphylaxis.
An allergy blood test is another option that can help a physician pinpoint allergens that may trigger a reaction. Blood tests are often used for patients who are not good candidates for skin testing, such as infants or individuals with skin disorders (e.g., eczema). They may also be useful to help confirm or rule out diagnoses.
The most commonly used blood test for allergy-related conditions is the radioallergosorbent test (RAST). This test looks for the presence of allergy-specific immunoglobulin E (IgE) in the bloodstream. During an allergic reaction, the body produces IgE antibodies to protect against what it mistakenly perceives to be a dangerous substance. The RAST test measures the amount of specific IgE produced to an individual allergen in a sample of blood. The level of IgE correlates to the sensitivity a patient has to the allergen. Related tests include MAST (multiple-antigen simultaneous testing) and PRIST (paper radioimmunosorbent test).
Treatment options for anaphylaxis
Anaphylaxis is a medical emergency that requires immediate treatment. Epinephrine is the most common drug used to reverse the symptoms of anaphylaxis. It constricts the blood vessels, prevents fluid leakage, opens the airways and raises blood pressure. It also quickly relieves the itching and skin flushing that is part of most episodes of anaphylaxis. Epinephrine usually is injected in the thigh.
Physicians may direct patients with a history of severe reactions to carry their own epinephrine injection kit to treat themselves in an emergency. This epinephrine is delivered through a device known as an auto-injector. The epinephrine that comes with the auto-injector allergy kit usually is good for 18 months. The kit is only available by prescription.
A patient must be trained to properly use the syringe, as injecting epinephrine into the wrong place in the body can have dangerous consequences. Patients can practice by using a training device. It is also a good idea to make sure a patient’s family, friends and coworkers know how to administer the epinephrine in an emergency situation. Parents should alert the staff at their child's school about their child's risk for anaphylaxis and confirm that staff members know how to administer epinephrine.
Epinephrine should be taken at the first sign of anaphylaxis because a reaction that is treated quickly is less likely to become severe. An ambulance should then be called to provide additional medical treatment. When epinephrine is not available, medical attention should be immediately sought, either through calling an ambulance or driving the patient to a hospital.
Though epinephrine is highly effective in treating anaphylaxis symptoms, its effect can be diminished by beta blockers or angiotensin-converting enzyme (ACE) inhibitors (which prevent blood vessel constriction). These drugs are prescribed to treat high blood pressure and some heart conditions. Patients who use these drugs should make sure a physician knows of their use. The physician may recommend alternative medications for treating heart or blood pressure conditions for patients at risk of severe allergic reactions.
Additional treatment may follow the epinephrine dose. Physicians may instruct patients in advance to take an antihistamine following the injection, if the person is able to swallow without difficulty. These patients may benefit from keeping an antihistamine in their allergy kit. This drug does not stop the reaction, but it can reduce the severity of symptoms.
Cardiopulmonary resuscitation (CPR) from a bystander may be required if a person becomes unconscious and stops breathing or does not have a pulse. Those who have suffered shock are likely to receive intravenous fluids and other medications to help support the actions of the circulatory system, including heart function. In rare cases, emergency personnel may perform a procedure to open an airway.
In about 10 percent of all cases, anaphylactic symptoms recur within four to 12 hours. This is known as a bi-phasic reaction. Antihistamines and corticosteroids may be prescribed to help reduce the chance of additional symptoms. Those who experience anaphylaxis should stay under medical supervision for a minimum of four to six hours after the attack subsides.
Prevention methods for anaphylaxis
Prevention of anaphylaxis is critical for those who have displayed symptoms in the past. As with all allergies, the best prevention method is to avoid the allergen altogether. For example, patients who are severely allergic to penicillin can use an alternative antibiotic to treat infections. A physician is likely to use an allergy skin test to ensure that these alternatives do not also trigger anaphylaxis.
Sometimes, advising a patient to simply avoid an allergen is not always practical. In such cases, additional safeguards may be prudent.
Allergy shot treatment (immunotherapy) is extremely effective in preventing some cases of anaphylaxis. The goal of immunotherapy is to build up a patient’s tolerance to the allergen. For example, patients at risk from insect stings would receive very low-dose injections of the insect venom until they build up a tolerance to it. Once the tolerance has been established, the likelihood of suffering an allergic reaction to a sting plummets. Some allergies do not respond well to immunotherapy, including food allergies and drug allergies.
Patients who have a history of anaphylaxis need to inform all healthcare providers – including dentists – of this history before undergoing medical care. Many experts also suggest patients wear a medical alert bracelet or pendant or carry a card that identifies allergies. This could save a patient’s life if he or she is unable to communicate during an anaphylactic episode.
Patients can also take commonsense measures to reduce the risk of anaphylaxis. Such steps include:
Always carefully check the ingredients on food labels to make sure they do not contain an allergen likely to cause a reaction. Also, ask about ingredients used in meals when eating in restaurants.
Limit gardening and keep stinging insects away by not wearing perfumes, colognes or bright-colored clothing. Wear long-sleeved shirts, pants and closed shoes when possible. Avoid walking barefoot, especially in grass.
Substitute vinyl gloves for rubber gloves. Inform physicians and dentists of latex allergies before any procedure and request that latex-free gloves be used. Also, request that care be exercised to prevent exposure to catheters, adhesives or other latex medical accessories.
In rare cases, exercise can trigger an allergy that leads to anaphylaxis. It appears that the digestion of certain foods – such as shrimp and celery – prior to exercise can be a contributing factor. Those who have experienced exercise-induced anaphylaxis should avoid strenuous activity for four to six hours after digesting the problem food.
Carrying an allergy kit with an epinephrine injection can also save a person who suffers from anaphylactic reactions.
Questions for your doctor
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to anaphylaxis:
How can I recognize an anaphylactic reaction?
Do my symptoms indicate that I have had an anaphylactic reaction?
Am I at risk for experiencing anaphylaxis again?
Will I experience the same symptoms during future episodes of anaphylaxis?
What tests will you use to determine the allergens that can cause me to have an anaphylactic reaction?
What dangers do I face during an anaphylactic reaction?
What should I do if I think I am having an anaphylactic reaction?
Do I have to go to the hospital if I have already treated myself with epinephrine?
Can you show me how to use an allergy kit? Where should I inject myself?
Should I carry an allergy kit at all times?
What steps can I take to prevent anaphylaxis?
Where can I get a training device for me and my family to practice injecting on?
Epinephrine by injection is the only effective immediate treatment.
Aminophylline, cortisone drugs or antihistamines, given after the epinephrine, help prevent the return of acute symptoms.