What Is a Severe Allergic Reaction?

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  • Written By: Alex Paul
  • Edited By: Angela B.
  • Images By: Laurent Hamels, Greg Friese, Defun
  • Last Modified Date: 13 June 2019
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A severe allergic reaction, otherwise known as anaphylaxis, occurs when the body overreacts to a foreign substance. Common causes of severe allergic reactions include peanuts, bee stings and medication. Symptoms of a severe allergic reaction vary, depending on the individual, but may result in serious problems such as swelling in the airways or heart failure.

An allergic reaction happens when the body tries to repel what it thinks is a potentially harmful substance. When the body detects a substance that shouldn’t be in the body, the immune system tries to destroy it. If the immune system reacts to a substance that isn’t harmful, such as dust or pollen, it is called an allergic reaction. Most allergic reactions don’t cause severe symptoms but instead result in minor problems such as a rash or sneezing.

A severe allergic reaction is much more serious and life-threatening. When a severe allergic reaction occurs, the person may develop difficulty breathing. He or she also may enter a state of shock, which results from low blood pressure. Allergic reactions can be caused by a variety of substances, so it can be difficult to determine what caused the reaction.


For anaphylaxis to occur, the body must already be “aware” of the substance from the past. This means there is usually no reaction the first time a person is exposed to a substance. The next exposure to that substance may result in a severe allergic reaction. A person also can be in contact with a substance many times before developing an allergy, whether mild or severe.

There are a number of potential symptoms of a severe allergic reaction. Many symptoms, such as facial swelling and dizziness, are not life-threatening. The time span over which the symptoms start also can vary from almost instantly to a few minutes or longer. Some of the most serious symptoms include swelling in the airways, which can cause difficulty breathing, and low blood pressure. There also is a chance that the heart may stop pumping.

A person suffering from a severe allergic reaction should seek immediate medical assistance. An ambulance should be called as soon as possible, because the symptoms may get worse if left untreated. Taking an antihistamine can reduce symptoms, although this may not be possible if the airways are blocked. An epinephrine pen, which is a medical tool used to inject a drug that can reverse allergic reactions, also can be used to treat severe symptoms, though additional medical treatment still should be sought.



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