Symptoms and Signs of Severe Allergic Reaction (Anaphylactic Shock)

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Medically Reviewed on 7/8/2022

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 a 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,

Some patients even feel like they're going to die. In addition, some individuals will produce

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 also termed adrenaline) to reduce a severe reaction, and it should be used if severe symptoms and signs 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 include many substances such as insect stings, some food allergies, certain chemicals such as sulfites, some medications, dyes, and many more.

What Are the Treatments for Anaphylactic Shock?

The treatments for anaphylactic shock are as follows:

  • Initial treatment is epinephrine (and have someone call 911) injected into the outer thigh (intramuscular dose, IM) even through clothing, if necessary, with a syringe or autoinjector like an EpiPen (fast action may be lifesaving):
    • In adults, 1 mg/ml aqueous solution, give a 0.3 mg IM
    • In children, 0.01 mg/kg in children less than 50 kg to 0.05 mg/kg in children over 50 kg IM
    • If available, O2
    • If available, IV antihistamine
    • If available, IV cortisone
    • albuterol
    • supportive care as needed (intubation, CPR, IV fluids, for example) usually done by EMS or ER caregivers

The most important treatment is epinephrine; the other treatments may not be available until EMS arrives or when the patient arrives at a hospital or well-equipped clinic. However, people who are likely known to be allergic to common items (peanuts, bee stings, for example) often carry an autoinjector with them wherever they go.


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