What causes anaphylaxis?

The immune system releases chemicals quickly after a sensitive person meets a trigger. This can affect the skin, airways, breathing, blood pressure and digestion at the same time. Food is a frequent trigger, including nuts, eggs, milk, fish and shellfish. Medicines and insect venom can also cause it. The reaction may begin after eating, taking, touching or being stung by the trigger; tiny exposures can matter for someone who is highly allergic. The exact trigger is not always found, and an episode can happen without a previously known allergy.

If anaphylaxis is suspected, use a prescribed adrenaline auto-injector immediately, if available, and call emergency services. Keep the person lying down with legs raised unless breathing is easier sitting up; do not let them stand or walk. A second auto-injector may be needed if symptoms do not improve, following its instructions. Medical assessment is still needed because symptoms can return after appearing to settle. After recovery, an allergy review can help identify triggers and create an avoidance and emergency plan.

Call emergency services at once for sudden difficulty breathing, throat or tongue swelling, wheezing, faintness, confusion, widespread hives with vomiting, or collapse after a possible allergen. Anaphylaxis can worsen rapidly, so do not wait to see whether symptoms pass. Anyone who has needed adrenaline should be monitored urgently, even if they feel better.

Ask which trigger is most suspected, whether testing or referral to an allergy specialist is appropriate, how to use an adrenaline auto-injector, and what should be included in your written emergency plan.