What is an allergy?

Updated September 2024

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An allergy is an overreaction by the body’s immune system to a normally harmless substance. Substances that can trigger an allergic reaction are called allergens.

People can be allergic to many things, such as pollen, mould, dust mites, animal dander or saliva, insect stings or bites, medication, food, and latex. Allergic disease also includes conditions such as eczema (atopic dermatitis), allergic rhinitis (hay fever), allergic conjunctivitis, and allergic asthma.

It is important that food allergies are not confused with food intolerance. Food intolerance does not involve the immune system.

Atopy is the genetic (inherited) tendency to develop allergic diseases. People with atopy are said to be atopic. When people with atopy are exposed to allergens, they can develop an immune reaction that includes inflammation (such as redness and swelling).

This inflammation can affect different parts of the body, such as the:

• nose and eyes – leading to allergic rhinitis and allergic conjunctivitis
• skin – leading to eczema or urticaria (hives)
• lungs – leading to asthma
• whole body or generalised response – leading to anaphylaxis (the most severe type of allergic reaction)

If you want to understand how exposure to an allergen leads to changes in your immune system that then cause symptoms, watch this video below. It uses food allergy as an example:

How common is allergy?

Allergic diseases are common in Australia – affecting over 6 million people – and are on the rise, for reasons that are unclear.

The most common allergic conditions in children are food allergies, eczema, asthma, and allergic rhinitis.

Up to 40% of children will experience some form of allergy during their lifetime.

Who is at risk of developing an allergy?

If you have a family history of allergic conditions, it makes sense to try to reduce the risk of your children developing allergic disease.

• If you or your partner has an allergy, your child has a 30% chance of inheriting the allergic gene and could, therefore, develop eczema, asthma, allergic rhinitis, or food allergy.
• If both parents have a history of an allergic condition, your child has a 40% to 60% chance of having some form of allergy.

If you have a history of allergy in the family, you are encouraged not to smoke during pregnancy and to breastfeed your baby for at least six months, if possible.

Signs and symptoms of an allergic reaction (including anaphylaxis)

The signs and symptoms you experience depend on the type of allergy you have. Allergies can be mild, moderate or severe.

Anaphylaxis is a severe allergic reaction that requires an immediate emergency response. It is often a sudden and severe allergic reaction that commonly affects more than one body system at the same time. Anaphylaxis can, however, sometimes just affect one body system. See the ASCIA Action Plan for Anaphylaxis. Foods, insects and medications (including those prescribed, over-the-counter or alternative therapies) are the most common causes of anaphylaxis.

Allergic reactions usually do not happen after the first exposure to an allergen but may happen on the next exposure. However, many people do not remember their first exposure to the allergen.

Diagnosis of allergy

Allergy testing can help work out which allergens cause your allergic asthma, allergic rhinitis and suspected allergic reactions to insects, foods, medications, or other allergens.

While there is no cure for allergies, there are many things people can do to avoid triggers, decrease the signs and symptoms, and improve the quality of their lives.

First, it is important to ensure that a diagnosis of allergy is accurate, as some conditions can mimic (look like) allergy. If you think you have an allergy, start by seeing your GP. You can then be referred to an allergy specialist if necessary.

Diagnosis and management may include:

• Allergen identification – identification of allergic triggers using a combination of what has happened when you had a reaction to the allergen and with allergy testing.
• Allergen avoidance of confirmed allergens where possible – important for people with allergies to foods, insects or drugs.
• Reduction of exposure to allergens – for people with allergic rhinitis, asthma, eczema or allergic conjunctivitis. Read more here.

Talk with your doctor for more information and look at evidence-based websites, such as those of hospitals, HealthDirect, or Better Health Channel. You can explore this website of Allergy & Anaphylaxis Australia (A&AA) and visit the website of our partner, the Australasian Society of Clinical Immunology and Allergy (ASCIA). ASCIA is the peak professional medical body for clinical immunology and allergy specialists in Australia and New Zealand, and it has a wide range of helpful information on the diagnosis and management of allergies. ASCIA and A&AA have partnered and formed the National Allergy Council that also has helpful evidence-based, easy to understand information.

It is important not to self-diagnose or depend on information from social media, newspapers, non evidence-based websites and sometimes even from family and friends.

If you think you have an allergy, it’s important to make an appointment with your GP for an accurate diagnosis, advice on preventative management, and emergency treatment. If you have moderate to severe allergy or live with the risk of anaphylaxis, get a referral from your GP to see an allergy specialist. You can read more in our page about allergy specialist appointments.

Treatment options

Allergy treatment options may include

• Medications:
  • Adrenaline (Epinephrine) – for emergency treatment of severe allergic reactions or anaphylaxis.  This may include the prescription of an adrenaline injector such as an EpiPen® or Anapen®. To learn more about adrenaline injectors click here.
  • Other medications – including antihistamines and corticosteroids in the form of nasal sprays, eyedrops, tablets, syrups or creams. To learn more about allergy treatment options click here.
• Immunotherapy:
  • Involves giving a small amount of the allergen (by injection or through the mouth) to try and decrease sensitivity to the allergen.
  • Immunotherapy can help increase the amount of allergen a person is exposed to before they start having signs and symptoms of an allergic reaction.
  • Allergen immunotherapy can be used to reduce the allergic response to grass pollen, dust mites and bee and wasp stings, for example.
  • Oral immunotherapy as a treatment for babies with peanut allergy is now happening in locations across Australia; however, it is not yet a standard treatment for other foods or people other than babies. Research in this area is ongoing.

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