• -Natalie

How long does it take for anaphylaxis to appear?

Anaphylaxis is a severe allergic reaction that can be life-threatening. Symptoms may involve hives, swelling, trouble breathing, fainting, and more. It is a systemic allergic reaction - involving more than one system of the body (respiratory, gut, skin, etc.)


How long does it typically take anaphylaxis to occur after exposure to an allergen? We have all heard of delayed reactions, sometimes occurring even up to 2 hours after exposure. But how common are these delayed reactions?


In a study presented at the American College of Allergy, Asthma, and Immunology conference, it was found that 86% of those who experienced anaphylaxis had symptoms within 30 minutes of exposure. The other 14% had symptoms after the 30 minutes, but it is not clear exactly when.


When broken down further by severity of the anaphylactic reaction (grades 1-3, with grade 3 being the most severe reaction), the percentages were found to be about the same.


Grade one anaphylactic reactions (the least severe) concluded that 85% experienced the reaction within 30 minutes.

As for grade two anaphylactic reactions, an even higher percentage of 90% experienced the reaction within 30 minutes.

As for the most severe cases of anaphylaxis, know as grade 3 reactions, 87% experienced the reaction within 30 minutes.


Thus, although delayed reactions can occur, it is important to realize that they are more rare than we might think.

In any case, it is important to always be prepared for anaphylaxis by carrying epinephrine everywhere and having an anaphylaxis action plan from your physician available at all times.


Information was taken from the American College of Allergy, Asthma, and Immunology conference in 2020.


This information is also confirmed by the World Allergy Organization: https://www.worldallergy.org/education-and-programs/education/allergic-disease-resource-center/professionals/anaphylaxis-synopsis#:~:text=Severe%20initial%20symptoms%20develop%20rapidly,with%20symptoms%20persisting%20for%20days.

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