Anaphylaxis is a severe, sudden, and potentially life-threatening allergic reaction that can affect several parts of the body at the same time. It can develop within minutes after exposure to an allergen and may cause difficulty breathing, swelling of the throat, a sudden drop in blood pressure, skin reactions, and problems with consciousness. Anaphylaxis is a medical emergency. Prompt treatment with epinephrine (adrenaline) can be lifesaving. Anyone who develops symptoms suggestive of anaphylaxis should receive emergency medical attention immediately. Anaphylaxis can occur after eating certain foods, taking medications, being stung by an insect, or coming into contact with other allergens. In some cases, a severe reaction can occur even when the amount of allergen involved is very small.
Symptoms can begin within seconds or minutes after exposure to an allergen, although they may occasionally appear later. The reaction can worsen rapidly. Common signs and symptoms include:
Anaphylaxis occurs when the immune system has an extreme reaction to a substance that it considers harmful. During the reaction, the body releases substances such as histamine and other inflammatory chemicals. These can cause widespread blood-vessel dilation, swelling, airway narrowing, and a sudden fall in blood pressure. Common triggers include:
Respiratory system: Swelling of the throat and narrowing of the airways can make breathing difficult. Wheezing, coughing, and a feeling of suffocation may occur.
Circulatory system: Blood vessels can widen suddenly, causing a dangerous fall in blood pressure. This can lead to dizziness, fainting, shock, or loss of consciousness.
Skin: Hives, redness, itching, and swelling may occur.
Digestive system: Abdominal cramps, nausea, vomiting, or diarrhea may develop.
Nervous system: Reduced blood flow to the brain can cause confusion, weakness, dizziness, or unconsciousness.
Anaphylaxis is primarily diagnosed based on the person’s symptoms, medical history, and the circumstances surrounding the reaction. A healthcare professional may ask:
What substance the person was exposed to
How quickly the symptoms developed
Whether the person has experienced allergies previously
What foods or medicines were recently consumed or taken
Whether an insect sting occurred
Whether similar reactions have happened before
There is no single test that should be relied upon to determine whether immediate treatment is necessary. Because anaphylaxis can progress rapidly, treatment should not be delayed while waiting for laboratory testing. After the emergency has been treated, an allergist may recommend allergy testing or other investigations to identify the likely trigger.
Epinephrine (adrenaline) is the first-line treatment for anaphylaxis. If a person has a prescribed epinephrine auto-injector and develops symptoms of anaphylaxis, it should be used immediately according to the person’s emergency action plan and the device instructions. Emergency medical services should be contacted immediately because symptoms can return or worsen even after initial improvement. Other treatments may be provided by healthcare professionals depending on the severity of the reaction. These can include:
Oxygen
Intravenous fluids
Additional medicines to support breathing or blood pressure
Bronchodilators for persistent wheezing
Antihistamines for certain symptoms
Corticosteroids in selected circumstances
Antihistamines and corticosteroids do not replace epinephrine as the first-line treatment for anaphylaxis.
If someone is experiencing symptoms of anaphylaxis:
Treat it as a medical emergency.
Use the person’s prescribed epinephrine auto-injector immediately, if available.
Call emergency medical services or seek emergency medical care immediately.
Have the person lie down with their legs elevated if this is comfortable and does not make breathing more difficult.
If vomiting or unconscious, place the person in an appropriate recovery position while maintaining breathing and monitoring them.
Avoid allowing the person to stand or walk unnecessarily, particularly if they are dizzy or weak.
If symptoms do not improve or return and a second prescribed epinephrine dose is available, it may be administered according to the person’s emergency plan and device instructions.
Continue monitoring the person until emergency medical professionals take over.
A person with suspected anaphylaxis should not be left alone.
Children can also experience anaphylaxis, particularly because of food allergies and insect stings. Parents and caregivers should learn to recognize warning signs such as:
Sudden hives or swelling
Difficulty breathing
Persistent coughing or wheezing
Swelling of the tongue or throat
Repeated vomiting
Dizziness or unusual weakness
Fainting or collapse
Schools, childcare providers, and other caregivers should be informed about a child’s allergies and know how to follow the child’s emergency action plan.
Yes. A person who has experienced anaphylaxis may have another reaction after being exposed to the same or a related trigger. Some people can also experience a biphasic reaction, in which symptoms return after initially improving. For this reason, medical evaluation and observation after an anaphylactic reaction are important. The appropriate observation period depends on factors such as the severity of the reaction, treatment required, and the person’s medical history.
Seek emergency medical attention immediately if a person develops symptoms suggesting anaphylaxis, particularly:
Difficulty breathing
Swelling of the tongue or throat
Wheezing
Fainting or severe dizziness
A sudden drop in blood pressure
Multiple symptoms involving different parts of the body after exposure to a possible allergen
Do not wait for symptoms to become severe before seeking emergency care. After recovering from an anaphylactic reaction, consultation with an allergist or immunologist is recommended to help identify the trigger and develop a plan to prevent and manage future reactions.
Yes. Anaphylaxis can rapidly become life-threatening because it may cause airway swelling, severe breathing problems, and a dangerous fall in blood pressure.
Epinephrine (adrenaline) is the first-line treatment for anaphylaxis. It should be administered promptly when anaphylaxis is suspected, followed by emergency medical evaluation.
No. Antihistamines may help relieve some allergy symptoms, but they do not replace epinephrine and should not be relied upon as the primary treatment for anaphylaxis.
Yes. Symptoms can sometimes return after initially improving. Medical assessment and observation following an anaphylactic reaction are therefore important.
The risk can often be reduced by identifying and avoiding known triggers, carrying prescribed epinephrine, and having an emergency action plan. People with a history of severe allergic reactions should work with an allergist or immunologist to manage their risk.
Medical Disclaimer:This article is intended for general educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Anaphylaxis is a medical emergency. If you or someone else has symptoms of anaphylaxis, seek emergency medical care immediately.
