An allergic reaction is the body’s response to an allergen. It can cause itching, rash, swelling, stomach symptoms, or breathing trouble. Some reactions stay mild, but some become serious and need urgent help.
What is an allergic reaction?
An allergic reaction happens when the immune system overreacts to something that is usually harmless. That trigger is called an allergen.
Common allergens include:
- foods such as nuts, eggs, milk, or shellfish
- insect stings or bites
- medicines
- latex
- pollen, dust, or animal dander
When the body reacts, it releases chemicals that can cause itching, redness, swelling, hives, tummy symptoms, or breathing problems.
What signs might you notice?
Signs of an allergic reaction can vary from person to person. Some reactions affect only the skin. Others affect breathing, alertness, or circulation.
Common signs include:
- itchy skin
- rash or hives
- swelling around the lips, eyes, or face
- sneezing or a runny nose
- tummy pain, nausea, or vomiting
- wheezing or trouble breathing
- dizziness or feeling faint
When does it become serious?
An allergic reaction becomes much more serious if the person develops breathing trouble, swelling in the tongue or throat, persistent dizziness, or collapse.
A severe allergic reaction is called Anaphylaxis. This is a medical emergency and needs urgent help straight away.
Call 000 in Australia if the person:
- has trouble breathing or noisy breathing
- has swelling of the tongue or throat
- becomes faint, floppy, or confused
- becomes Unresponsive
- gets worse quickly after exposure to a likely allergen
What should you do in first aid?
If you think someone is having an allergic reaction:
- Stay calm and reassure the person.
- Move the allergen away if it is safe to do so.
- Ask if they have a known allergy and whether they carry an Adrenaline Auto-Injector.
- If you know the brand, check whether it is an EpiPen or Anapen, and help them use it if needed.
- Watch their breathing and how alert they are.
- Call
000if symptoms are severe, getting worse, or you are unsure.
The medicine inside an adrenaline auto-injector is Epinephrine, also called adrenaline.
Do not give food or drink if the person has swelling, trouble swallowing, or trouble breathing.
What if the person becomes unresponsive?
If the person becomes unresponsive, their breathing becomes the main priority.
- If they are unresponsive but breathing normally, follow the Recovery Position.
- If they are not breathing normally, start CPR and follow emergency call guidance.
How is this page different from the others?
This page is the broad overview page for the term allergic reaction. It explains what the phrase means, common triggers, and when the situation becomes more serious.
If you want the page that focuses mainly on the signs you might notice, read Allergic Reactions.
If you want the device overview page, read Adrenaline Auto-Injector.
If the reaction is severe or life-threatening, read Anaphylaxis.
Summary
An allergic reaction is the body’s overreaction to an allergen. It may cause itching, swelling, rash, tummy symptoms, or breathing problems. Some reactions stay mild, but serious reactions can become anaphylaxis and need urgent help. In first aid, the key steps are to notice the signs early, help with prescribed medication if available, and call 000 if the reaction is severe or getting worse.
Sources reviewed
- ASCIA: anaphylaxis information and current device links
- Triple Zero: official emergency calling guidance
Reviewed against current Australian allergy, first aid and emergency guidance by the First Aid Glossary Editorial Team. This article is general information and does not replace a person’s current ASCIA Action Plan, device instructions, emergency-operator directions, professional medical advice or hands-on first aid training.
