What is allergy?

Allergy occurs when a person reacts to substances in the environment that are harmless to most people.These substances are known as allergens. Allergies can be caused by a number of different mechanisms.Allergies which cause symptoms shortly after exposure to the allergen are caused by antibodies called IgE-antibodies and only this type of allergy (IgE-mediated allergy) can be investigated in the laboratory.Allergies affect around one in five people in Australia and New Zealand and are increasingly common. There are many causes of allergy, and symptoms vary frommild to potentially life threatening.

Common sources of allergens include:

• Dust mites
• Pets
• Arthropod bites and stings (e.g bee, wasp & ant stings, tick bites)
• Pollens
• Moulds
• Foods
• Medications and other chemicals

Who suffers from allergies?

Allergic disorders affect around one in five people inAustralia at some point in their life. They may affect people of any age, and reactions may range from mild to severe. Fortunately if you have an allergy, diagnosis and treatment options are usually available.

What are the symptoms of an allergy?

The symptoms that you experience from an allergic reaction will depend on the type of substance you are allergic to and how you have been exposed to the substance. For example, when allergens such as pollens, dust mites, mould spores, or animal dander are inhaled, you may experience symptoms in the nose, eyes, sinuses, throat and chest (including asthma in some people). Allergy to foods may lead to hives, swelling, breathing and abdominal symptoms, or even life-threatening allergy (anaphylaxis). Allergic reactions can involve several parts of the body at the same time.

Regions affected may include:

• Nose and eyes: when allergens are breathed in the lining of your nose produces lots of mucus and may become swollen and inflamed. This causes your nose to run and itch, and violent sneezing may occur.Other symptoms can include watery and itchy eyes, and an itchy throat.
• Airways and chest: asthma can sometimes be triggered during an allergic reaction. Bronchial inflammation and narrowing (bronchospasm) may cause wheezing.
• Swellings: leaking of fluid from blood vessels into the tissues causes swellings (angioedema). If this affects the tongue or throat, it can cause obstruction of the upper airway leading to breathing difficulty.
• Stomach and bowel: ingesting an allergen can cause nausea, abdominal pain, vomiting & diarrhoea.
• Skin: Urticaria (hives) can be caused by allergy. Eczema(atopic dermatitis) can be exacerbated by allergies.
• Anaphylaxis: this is a severe allergic reaction which can be life threatening and can involve airway obstruction from swellings and bronchospasm from wheeze, which can cause breathing difficulties; it often also involves skin symptoms (urticaria) and abdominal symptoms and in some cases, blood pressure may drop dramatically (hypotension) leading to collapse.

How is an allergy diagnosed?

There are a number of ways that your doctor may choose to investigate your allergy. Your doctor will be able to advise on which course of action is appropriate for your situation. Blood tests for investigation of IgE-mediated allergy are available at our Pathology collection centres with a doctor referral. Such tests in isolation do not diagnose allergy: interpretation of test results is complex and must be done by an experienced medical practitioner in the context of clinical information.