HealthInfo Waitaha Canterbury

Overview of allergies

Mate pāwera

 

When you have an allergy, your immune system overreacts to a substance that is harmless to most people. Your body's immune system treats the substance (known as an allergen or trigger) as an invader.

To defend itself against the allergen, your body produces antibodies called immunoglobulin E (IgE). These antibodies cause certain cells in your body to release chemicals such as histamine into your bloodstream to fight off the invader.

The release of these chemicals causes an allergic reaction. Your symptoms vary according to the part of your body affected but they can include sneezing, watery eyes, itching, rash and raised weals (hives) on your skin. Extreme allergic reactions can be life-threatening and needs immediate treatment. This is called anaphylaxis.

Causes of allergies

While you do not directly inherit an allergy, you may inherit a tendency to be allergic and develop allergic diseases. This tendency is called being atopic. Allergies only start if you're exposed to an allergen. Once you develop a sensitivity to an allergen, an allergic response is set off every time you're exposed to the allergens that affect you.

Substances in the environment that can cause an allergic reaction are called allergens. Common allergens include:

• the droppings of house dust mites
• pollen, particularly from grass, trees and weeds
• animal dander (skin, scales or flakes from animals)
• metals such as nickel in watch bands, earrings or belt buckles
• latex in rubber products
• some moulds
• insect bites and stings
• household chemicals such as those in hair dyes and detergents
• medicines
• foods such as peanuts, dairy, eggs and seafood.

True food allergies aren't common. Most reactions to food are more likely to be food intolerance, which doesn't involve your body's immune system.

Cigarette smoke is often considered a cause of allergies, but it's actually an irritant rather than an allergen. That means it doesn't cause an allergy but makes an existing allergy worse.

Symptoms of allergic conditions

Depending on the type of allergens and where the allergens enter your body, they can cause different allergic reactions and conditions. These include:

• allergic rhinitis (hay fever)
• allergic contact dermatitis
• allergic conjunctivitis
• asthma
• food allergies
• anaphylaxis.

Symptoms can range from mild to severe. Typically, symptoms happen within minutes to an hour after you're exposed to a particular allergen.

• Hay fever affects your eyes and nose when you inhale allergens. Symptoms include sneezing, runny nose, watery and itchy eyes, irritated and itchy throat and sometimes, a stuffy, blocked nose.
• Allergic contact dermatitis is caused by your skin coming into contact with an allergen such as nickel. Symptoms include red, scaly skin that itches.
• Allergies to some foods, insect bites or stings can cause hives (urticaria), which are raised red, itchy patches on your skin and other symptoms such as nausea or vomiting, swelling around your lips, face and eyes, diarrhoea (runny poo) or sneezing.
• Anaphylaxis is a severe allergic reaction. It can involve your whole body and is a life-threatening condition. It requires immediate life-saving medicine such as adrenaline.

Diagnosing allergies

It's important to talk to your general practice team if you think you or your tamaiti (child) may have an allergy to something. There are many causes of allergies, and some symptoms may be due to other conditions.

Your general practice team will ask you or your tamaiti about allergic symptoms, any known triggers and if you've been exposed to possible new triggers such as new food, medicine or pets.

When your symptoms appear soon after you've been exposed to a particular allergen, it's easy to identify which allergen is causing your reaction. But if the cause is unknown, you might need other diagnostic tests. This might include a skin prick test or a blood test to test for the presence of an antibody (IgE) that causes an allergic reaction.

Your general practice team may also refer you or your tamaiti to a paediatric clinic or allergy specialist for further tests if the cause is still unclear. Read more about allergy testing.

Treating allergies

If possible, avoiding the allergen that causes your allergy is the best treatment. Other treatments depend on the type of allergy you have and include:

• antihistamines
• steroid tablets
• steroid nasal inhalers or decongestant nasal sprays
• medicated or non-medicated eye drops
• moisturiser (emollient) or corticosteroid creams
• adrenaline – usually in an autoinjector called EpiPen.

If these treatments do not work, particularly for hay fever, desensitisation treatment known as allergen Immunotherapy may be suitable for you.

Preventing an allergic reaction

The best way to prevent an allergic reaction is to identify the substances that trigger your allergy and try to avoid them. Read about self-care for allergies.

  HealthInfo recommends the following pages

• Allergy New Zealand

  Allergy New Zealand provides information, education and support for people with allergy, parents of tamariki (children) with allergy, teachers and healthcare professionals.

• Australasian Society of Clinical Immunology and Allergy – What is allergy?

  Detailed information about allergies.

• Health Information Translations – Allergies

  Factsheets about allergies in several languages.

• KidsHealth – Allergy

  Information about allergies in tamariki.

Content shared between HealthInfo Canterbury, KidsHealth and Health Navigator NZ as part of a National Health Content Hub collaborative. Page created July 2022.

Sources

Page reference: 672378

Review key: HIALL-38559