How quickly anaphylaxis can develop

Do not wait to see whether suspected anaphylaxis settles. A reaction can move from itching, flushing or stomach discomfort to airway swelling, breathing difficulty or circulatory collapse over a short period.

Onset depends on the trigger, how it entered the body and the person's response. Reactions after an injected medicine or insect sting may become apparent very quickly, while reactions associated with food can sometimes take longer to declare themselves. Timing alone cannot show how severe a reaction will become.

Early features may involve the skin, mouth, gut, lungs or circulation. Anaphylaxis commonly presents with combinations such as widespread hives plus wheezing, or sudden vomiting plus faintness after a likely allergen. A person may also have dangerous breathing or circulation symptoms without a rash.

Use the person's prescribed adrenaline auto-injector as soon as anaphylaxis is suspected, following its instructions, then call local emergency services. Note the time it was given. Antihistamines may help some skin symptoms, but they do not replace adrenaline for breathing problems or impaired circulation.

Have the person lie down and keep them from standing or walking. Someone with difficult breathing may sit with legs extended; someone vomiting or unconscious but breathing should be placed on their side. Remain with them, monitor breathing and follow instructions from the emergency call handler.

Treat throat tightness, tongue swelling, a hoarse voice, wheezing, noisy breathing, persistent coughing, dizziness, confusion or collapse after a possible allergen as an emergency. Sudden symptoms affecting different body systems can also indicate anaphylaxis.

A person needs emergency assessment even if symptoms improve after adrenaline, because symptoms can continue or recur. If the cause is uncertain, clinicians can assess the episode and arrange follow-up rather than relying on speed of onset to identify the trigger.

Ask your doctor which early symptoms should activate your emergency plan and how to recognise changes in breathing or alertness. Confirm how to store and use your injector, when it needs replacement, which suspected exposures to avoid and whether allergy testing could help clarify the trigger.