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What are allergies and why do they develop?

A man blows his nose, his eyes red and irritated.
Inhaled allergens like pollens or perfumes can cause a runny, itchy nose and itchy eyes.

Allergies are very common, with around 1 in 5 people in Australia experiencing an allergy during their lives.

What causes allergic reactions?

The things that people are allergic to, called allergens, are usually everyday substances that other people can tolerate just fine. Common allergens include peanuts and other nuts, animal hair, pollen, crustaceans and fish, mould, dust mites, insect stings and medications.

When a person is allergic to a substance, their immune system reacts to it when it touches their skin, they breathe it in, or they ingest it. Some allergic reactions are driven by antibodies. Antibodies attach themselves to cells in the body called mast cells. When the allergen comes into contact with the antibodies, the mast cells release substances like histamine, which cause the inflammation and swelling typical of an allergic reaction.

Allergic reactions can affect the nose, eyes, sinuses, throat, skin, stomach, bowel and lungs.

The nose, eyes, sinuses and throat are affected by allergens that are inhaled. During an allergic reaction, these areas can become swollen, inflamed or itchy, with extra mucus produced in the nose and fluid in the eyes.  

The lungs are also affected by allergens that are inhaled. Some people with asthma find their condition is triggered by allergens; however, it is possible to have asthma that is not caused by allergens, too.

The stomach and bowel are affected by allergens that are in foods or liquids that we ingest. Symptoms of an allergic reaction triggered by food or drink can include abdominal upsets like nausea, vomiting, or abdominal pain. Eczema and asthma can also be triggered by ingested allergens.

Hives on the skin can be caused by allergens that have been ingested or allergens that have come into contact with the skin.  

Who develops allergies?

It’s possible for everyone to develop an allergy. Some people identify allergies early in life, while others develop allergies as they age.

Some people are genetically predisposed to developing allergies. This means they’ve inherited a tendency to be allergic to things from their family. People with atopy, or atopic people, may have eczema, hay fever or asthma. Some have all three of these conditions.

Studies show that introducing food that might cause an allergic reaction within a baby’s first 12 months can help prevent them from developing an allergy to that food. The Australasian Society of Clinical Immunology and Allergy has a guide for parents introducing food to their babies.

An array of foods that are common allergens sit on a table, including strawberries, nuts, grains, eggs, prawns and chocolate.

Are allergies serious?

The severity of an allergic reaction can vary from mild to severe, changing from person to person and in one person from each exposure to an allergen.

Some allergic reactions, like watery eyes from hay fever, cause irritation or discomfort, but are not severe.

Other allergic reactions, like anaphylaxis, can be immediately life-threatening, and should be taken extremely seriously. Anaphylaxis is a severe allergic reaction which, among other symptoms, can cause a person’s face, lips, tongue and throat to swell, and might cause them to stop breathing. You can read more about anaphylaxis and how it is treated here.

What should I do if I think I have an allergy?

If you think you’re having an allergic reaction right now, seek appropriate treatment in line with the severity of your reaction.

If you think you are experiencing an anaphylactic reaction, call Triple Zero (000) for an ambulance.

If your symptoms are not severe, like a rash, watery eyes or itchy nose, see your pharmacist or call 13 HEALTH (13 43 25 84) for advice on over-the-counter medications that might help ease your symptoms.

Allergies can be managed. If you think you are allergic to something, see your GP about creating a plan to identify your allergens so that you can minimise your exposure and understand the appropriate medications available to help manage your condition if necessary.

Adverse reaction, sensitivity, intolerance or allergy?

Other conditions can have similar symptoms to allergies. Adverse reactions (when a person’s body does not react to a product, like a medicine, in the way that is intended), intolerances and sensitivities might all cause similar symptoms.

More information

You can find more information about allergies at the links below.

Australasian Society of Clinical Immunology and Allergy

Allergy and Anaphylaxis Australia

What is a food allergy?

Health Direct: Allergies

Last updated: 26 April 2018