What are allergies and hypersensitivities?

A hypersensitivity reaction is an overreaction of your immune system to something that normally wouldn't cause a reaction. Allergies are a sub-type of hypersensitivity.

Types of hypersensitivity reaction

There are different types of hypersensitivity reactions based on which parts of your immune system are involved.

• Type I reactions involve your mast cells (a type of white blood cell). They usually start within a few minutes of exposure to an allergen but sometimes they can take a few hours to develop. This type of reaction is an allergy and are usually mild but can sometimes become a serious reaction called anaphylaxis.
• Type II and III reactions involve the formation of IgG antibodies and happen when something triggers your immune system to attack parts of your own body. This can cause autoimmune diseases that range from mild to severe.
• Type IV reactions involve your T cells (another type of white blood cell). They are also called 'delayed hypersensitivity reactions' and happen 48 to 72 hours after exposure to the cause. Some examples of type IV reactions are contact dermatitis, some lung conditions, type I diabetes and organ transplant.

What is an allergy ?

An allergy is a Type I reaction that happens soon after you have been exposed to an allergen (substance that you are allergic to).

Common substances that you may be allergic to are:

• foods (including egg, fish and shellfish, nuts, wheat, dairy, soy)
• cat and dog dander
• grasses and pollen
• dust mite
• some medicines
• insect and mite bites
• latex (rubber)

Allergies and hypersensitivities are not the same. An allergy is a type of hypersensitivity. Not all hypersensitivities are allergies.

What are the symptoms of allergies?

Symptoms of allergies depend on the cause and severity of your allergy. Allergy symptoms can range from mild to life-threatening.

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:

• breathing problems
• swollen tongue, lips and face
• swelling or tightness in the throat
• difficulty talking or a hoarse voice
• wheezing and coughing
• abdominal pain and vomiting
• dizziness and possible 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 needs immediate treatment with an injection of adrenaline. If you or someone with you is having an anaphylactic reaction and they have an adrenaline autoinjector (brand names include EpiPen and Anapen), give them a shot of adrenaline.

Learn about first aid for anaphylaxis and how to use an adrenaline autoinjector.

See your doctor if you have mild or moderate allergy symptoms.

How are allergies diagnosed?

Your doctor will ask about your symptoms and perform 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?

Treatment for allergies depends on the type and severity. Talk to your doctor about which treatments might be best for you.

Your doctor may refer you to an allergy specialist for more tests and treatment.

Medicines

Allergies can be treated with antihistamine medicines. These may be given as:

• a tablet
• a nasal spray
• syrups
• eye drops

Corticosteroid medicines can help treat allergies. These can be given as a:

• nasal spray
• tablet
• inhaler
• skin ointment or cream
• injection

Adrenaline (epinephrine) for anaphylaxis

Anaphylaxis needs emergency treatment with adrenaline (epinephrine). People with severe allergies should carry an adrenaline autoinjector at all times.

Allergy action plan

People who have severe allergies should have an allergy action plan to help them and others know what to do in an emergency.

Allergen immunotherapy or desensitisation

Allergen immunotherapy is a way to desensitise you to an allergen. This therapy is usually started by a specialist immunologist. Treatment may be needed for at least 3 years.

Can allergic reactions be prevented?

Allergic reactions can't always be prevented.

You can lower your chances of allergic reactions by avoiding what you are allergic to.

You can reduce allergen exposure by:

• removing any products with the allergen from your home
• asking about how food is prepared and what ingredients are used when eating out
• reading labels on packaged food carefully to check for allergens
• showering and washing your hair after being outside, especially during pollen season
• washing your sheets and bedding every week in hot water (over 60ºC) to kill dust mites
• dusting surfaces every week with a damp cloth to reduce dust in your home

Resources and support

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

Allergy & Anaphylaxis Australia has lots of helpful guides on living with allergies.

The Sydney Children's Hospital Network has a factsheet about allergic reactions and allergy test.

Languages other than English

Health Translations has information about anaphylaxis and a first aid plan for anaphylaxis in many languages.

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with you 24 hours a day, 7 days a week.