Symptoms and Signs of Severe Allergic Reaction
(Anaphylactic Shock)

Medical Author:
Medically Reviewed on 3/11/2019

Doctor's Notes on Severe Allergic Reaction
(Anaphylactic Shock)

A severe allergic reaction (anaphylactic shock) is a life-threatening immune response usually due to severe allergic reactions. Signs and symptoms of severe allergic reaction can come on quickly or gradually but the majority come on suddenly. Severe and life-threatening signs and symptoms are difficulty breathing and loss of consciousness (shock). Almost immediately after exposure to a particular allergen, feeling of warmth, difficulty swallowing, swelling (in the face, eyelids, lips, tongue and throat), nausea and/or vomiting, diarrhea, abdominal cramping, bloating, anxiety and confusion may appear suddenly; some patients even feel like they’re “going to die”. In addition, some individuals will produce hives, welts or wheals with severe itching, cough, hoarseness and may appear pale. Any person with some of the above symptoms is probably experiencing a severe reaction and 911 needs to be called immediately; some individuals carry medication (for example, epinephrine) to reduce a severe reaction and it should be used if severe symptoms occur even before emergency responders arrive.

The cause of severe allergic reaction is the body’s overactive response to an antigen. It produces chemicals called immune mediators such as histamine that cause the life – threatening symptoms to develop. Triggers or antigens that cause the immune system to overreact includes many substances such as insect stings, some food allergies, certain chemicals such as sulfites, some medications, dyes and many more.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.