See also:

Anaphylaxis is usually defined as an acute systemic allergic reaction with compromise airways, breathing and/or circulation.  Systemic here means that the reaction is not limited to just one body system (skin, GI, respiratory etc) but spreads to others.  It is usually – but not exclusively – mediated by IgE-antibodies.

There are however 5 different international definitions – not all include systemic, and of course not all systemic are anaphylaxis (for example skin and gut, 2 systems, not usually called anaphylaxis – except NIAD definition in US, which specifies “persistent gut symptoms”).  Respiratory involvement alone sometimes not called anaphylaxis by experts, even when treated as such! 3 definitions use “life threatening” but that is somewhat subjective and poses the danger of delaying appropriate management until the reaction is already advanced. 

Use of the word “anaphylactic” is discouraged in the Resus council guideline, unless talking about anaphylactic shock, as it is misused to describe patients at risk of anaphylaxis (they may describe themselves as such), whereas this is actually anyone with a type 1 allergy.  

Anaphylactoid reactions are immediate systemic reactions that mimic anaphylaxis but for which an IgE-mediated immune mechanism can not be established – most people don’t bother trying to make a distinction now.

Resuscitation Council definition (2021):

  • Sudden onset, rapid progression
  • Airway/breathing/circulation problems (not specified)
  • “Life threatening” includes:
    • hoarse voice, stridor
    • wheeze, work of breathing, cyanosis, fatigue
    • Signs of shock (presumably pale, clammy), low BP, confusion, reduced consciousness
    • (not tongue swelling or persistent cough)


Where no cause identified consider:

Rare allergens, eg galactose alpha-1,3 galactose , pigeon tick bite (Argax reflexus), wheat-dependent exercise-induced anaphylaxis, Anisakis simplex allergy.

Differential includes mast cell disorders, asthma, panic attacks, conversion disorder, globus hystericus, vocal cord dysfunction, scombroid poisoning, vasoactive amine intolerance, carcinoid syndrome and phaeochromocytoma.