There is no single set of diagnostic criteria that will identify all anaphylactic reactions; there are a range of symptoms that are not unique to anaphylactic reactions.

 Anaphylaxis is likely when all of the following criteria are met:

• Life-threatening airway and /or breathing and/or circulatory problems
• Sudden onset and rapid progression of symptoms
• Skin and/or mucosal changes such as urticaria, flushing or angioedema (tissue swelling, particularly around face/ mouth/ tongue)

The key feature of an anaphylactic reaction is the sudden onset and rapid progression of symptoms.

Patients may commonly describe a sense of impending doom or anxiety before showing physical symptoms of anaphylaxis.