Anaphylaxis usually starts within minutes to two hours of exposure to a trigger such as a food, insect sting, medication, or latex. The classic red flags are breathing problems (wheezing, noisy breathing, persistent cough, or a feeling that the throat is closing), swelling of the lips, tongue, throat, or face, a sudden widespread itchy rash or hives, a rapid drop in blood pressure causing lightheadedness, collapse, or loss of consciousness, and gut symptoms like cramping, vomiting, or diarrhoea. A sense of impending doom is also commonly described.
Anaphylaxis is a medical emergency. If someone has signs affecting their breathing, circulation (faintness, pale or clammy skin), or two or more body systems at once, treat it as anaphylaxis. Give an adrenaline (epinephrine) auto-injector into the outer thigh if one is prescribed and available, then call your local emergency number. Lay the person flat and raise their legs unless they are struggling to breathe, in which case let them sit up.
Even if symptoms improve after adrenaline, the person still needs urgent medical assessment because reactions can return hours later (a biphasic reaction). Do not let them get up suddenly. A licensed doctor should review the event and arrange an allergy specialist referral and an emergency action plan.