Anaphylactic reactions are sudden, widespread, potentially severe and life-threatening allergic reactions.
Anaphylactic reactions often begin with a feeling of uneasiness, followed by tingling sensations and dizziness.
People then rapidly develop severe symptoms, including generalized itching and hives, swelling, wheezing and difficulty breathing, fainting, and/or other allergy symptoms.
These reactions can quickly become life threatening.
Avoiding the trigger is the best approach.
Anaphylactic reactions require emergency treatment.
(See also Overview of Allergic Reactions.)
Like other allergic reactions, an anaphylactic reaction does not usually occur after the first exposure to an allergen (the substance that triggers an allergic reaction) but may occur after a person is exposed to the allergen again. However, many people do not recall a first exposure. Any allergen that causes an anaphylactic reaction in a person is likely to cause that reaction when the person is exposed again, unless measures are taken to prevent it.
Causes of Anaphylactic Reactions
Anaphylactic reactions are most commonly caused by the following:
Medications (such as penicillin)
Insect stings and animal venoms
Certain foods (particularly eggs, seafood, and nuts)
Latex
But they can be caused by any allergen.
Anaphylactoid reactions
Anaphylactoid reactions resemble anaphylactic reactions. However, anaphylactoid reactions, unlike anaphylactic reactions, may occur after the first exposure to a substance.
Also, anaphylactoid reactions are not allergic reactions because immunoglobulin E (IgE), the class of antibodies involved in allergic reactions, does not cause them. Rather, the reaction is caused directly by the substance.
The most common triggers of anaphylactoid reactions include
Iodine-containing substances that can be seen on x-rays (radiopaque contrast agents)
Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs)
Opioids
Monoclonal antibodies (manufactured antibodies that target and suppress specific parts of the immune system)
Exercise
Symptoms of Anaphylactic Reactions
Anaphylactic and anaphylactoid reactions typically begin within 15 minutes of exposure to the trigger. Rarely, reactions begin after 1 hour. Symptoms range from mild to severe, but each person usually has the same symptoms each time.
The heart beats quickly. People may feel uneasy and become agitated. Blood pressure may fall, causing fainting, and may become dangerously low (a condition called shock). Other symptoms include dizziness, itchy and flushed skin, coughing, a runny nose, sneezing, hives, and swelling of tissue under the skin (angioedema). Breathing may become difficult and wheezing may occur because the throat and/or airways narrow or become swollen. People may have nausea, vomiting, abdominal cramps, and diarrhea.
An anaphylactic reaction may progress so rapidly that people collapse, stop breathing, have seizures, and lose consciousness within 1 to 2 minutes. A severe reaction may be fatal unless emergency treatment is given immediately.
Symptoms may recur 4 to 8 hours after exposure to the allergen or later. Such symptoms are usually milder than they were at first, but they can be more severe or fatal. Doctors observe people for several hours after the first reaction.
Diagnosis of Anaphylactic Reactions
A doctor's evaluation
Sometimes blood tests
The diagnosis of anaphylactic reactions is usually obvious based on symptoms such as the following:
Symptoms of shock (such as low blood pressure, confusion, cold and sweaty skin, and a weak and rapid pulse)
Respiratory symptoms (such as difficulty breathing, a gasping sound when breathing in, and wheezing)
Two or more other symptoms of possible anaphylaxis (such as angioedema, hives, and nausea or other digestive symptoms)
Because symptoms can quickly become life threatening, treatment is begun immediately, without waiting for tests to be done.
To confirm the diagnosis, doctors may do blood tests to measure certain substances that increase soon after an anaphylactic reaction. However, these tests are usually unnecessary.
Treatment of Anaphylactic Reactions
Sometimes a breathing tube
Sometimes fluids given intravenously
Antihistamines and other medications
epinephrine may be needed.
If breathing is severely impaired, a breathing tube may be inserted into the windpipe (trachea) through the person’s mouth or nose (intubation) or through a small incision in the skin over the trachea, and oxygen (if needed) is given through the breathing tube.
Blood pressure often returns to normal after epinephrine is given. If it does not, fluids are given intravenously to increase the volume in the blood vessels. Sometimes people are also given medications that help increase blood pressure.
Antihistamineshistamine-2 (H2) blockers
A corticosteroid is sometimes given to help prevent symptoms from recurring several hours later, although whether this treatment is necessary is unclear.
Prevention of Anaphylactic Reactions
Avoiding the allergen is the best prevention. People who are allergic to certain unavoidable allergens (such as insect stings) may benefit from long-term allergen immunotherapy. For allergen immunotherapy, people are given progressively larger doses of the allergen to try to teach the immune system not to react to that allergen.
