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Allergies and hypersensitivities

4-minute read

What is an allergy?

An allergy is when your immune system reacts to something that is harmless to most people.

Substances that cause allergies are called ‘allergens’. Common allergies include:

What is a hypersensitivity reaction?

A hypersensitivity reaction is an overreaction of your immune system to something that would not usually cause an immune response. This leads to allergy symptoms.

There are different types of hypersensitivity reactions.

  • Type I reactions usually develop within a few minutes of exposure to an allergen, but can occasionally develop over a few hours. They are mostly mild but can sometimes develop into a severe reaction called anaphylaxis.
  • Type II and III reactions are immune reactions where your body’s own immune system attacks parts of your body. This can cause autoimmune diseases that vary from mild to severe.
  • Type IV reactions are also called ‘delayed hypersensitivity reactions’. These reactions can happen from 12 to 72 hours after exposure to the allergen. For example, contact dermatitis, some lung conditions, type I diabetes and organ transplant rejection.

What are the symptoms of allergies?

Symptoms of allergies depend on what you are allergic to and how severe your allergy is. Symptoms can range from mild to life-threatening.

Some of the symptoms or conditions caused by allergies include:

  • hay fever (runny nose, itchy and watery eyes)
  • eczema (dry, red, itchy skin)
  • hives (a bumpy skin rash)
  • asthma (wheezing, coughing and difficulty breathing)

A severe type of allergic reaction called anaphylaxis can cause:

  • difficulty breathing
  • noisy breathing
  • swollen tongue, lips and face
  • swelling or tightness in the throat
  • difficulty talking or a hoarse voice
  • wheezing and coughing
  • tummy pain and vomiting
  • dizziness
  • collapse

Watch this video from Allergy & Anaphylaxis Australia for more information about how to recognise signs and symptoms of an allergic reaction.

Video not working? View it here.

When should I see my doctor?

Anaphylaxis is an emergency. If you think someone is having an anaphylactic reaction call an ambulance on triple zero (000).

Anaphylaxis needs immediate treatment with an injection of adrenaline. If you or someone with you is having an anaphylactic reaction and they have an adrenalin autoinjector (brand names include EpiPen and Anapen), give them a shot of adrenaline.

See your doctor if you have mild or moderate allergy symptoms. There are treatments available and ways to manage allergies to help you feel better.

How are allergies diagnosed?

Your doctor will ask about your symptoms and may do a physical examination. They will ask about your overall health and the health of your family.

Your doctor may suggest allergy testing. These tests can help find out what you are allergic to.

How are allergies treated?

Talk to your doctor about what treatments may suit you.

Your doctor may refer you to an allergy specialist for further treatment.


Allergies can be treated with antihistamine medicines. These can be given as a tablet, nasal spray or eye drops.

Corticosteroid medicines are sometimes used to treat allergies. Depending on your symptoms, these can be given as a nose spray, inhaler, cream or ointment for your skin.


Allergen immunotherapy is a type of treatment for allergies. It helps to stop the body overreacting to allergens.

Adrenaline (epinephrine) for anaphylaxis

Anaphylaxis needs emergency treatment with adrenaline (epinephrine). People with severe allergies should carry an adrenaline autoinjector (brand names include EpiPen and Anapen) at all times.

Allergy action plan

People who have severe allergies will need an action plan which tells them what to do in an emergency.

Can allergic reactions be prevented?

People with severe allergies need to avoid the substances they are allergic to.

If you have hay fever or eczema, you should try to reduce exposure to the things you are allergic to.

There are guidelines from the Australasian Society of Clinical Immunology and Allergy (ASCIA) on infant feeding and allergy prevention.

Talk to your doctor about steps you can take to avoid and prevent allergies.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: June 2022

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