Allergies

Allergies are very common, affecting about 1 in 3 New Zealanders at some time in their lives.

Key points about allergies

  1. An allergy happens when your immune system overreacts to substances called allergens. Your body treats an allergen as an invader and begins to create antibodies against it.
  2. Common allergens include house house dust mites, grasses, pollen, pets, foods, some medicines, insect stings, latex and moulds. 
  3. Symptoms of allergies range from mild hay fever to potentially life-threatening reactions called anaphylaxis.
  4. Children have more allergies than adults. As your immune system matures, some allergies disappear, eg, some food allergies.
  5. The best way to prevent symptoms is to avoid what triggers your allergy. Talk with your healthcare team to find out what other treatments will help you.

Anaphylaxis is a severe allergic reaction and must be treated as a medical emergency, requiring immediate treatment and urgent medical attention. If you or someone you care for experiences the symptoms of anaphylaxis below, give adrenaline (EpiPen) if available and call 111 for an ambulance.

  • Swelling of your tongue
  • Tightness in your throat
  • Difficulty breathing or wheezing
  • Difficulty talking or hoarse voice
  • Dizziness or collapse
  • Pale and floppy (in young children)

What is an allergic reaction?

When you have an allergy, your immune system overreacts to a substance that, to most people, is harmless. 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 in an attempt to fight off the invader.

The release of these chemicals causes an allergic reaction. Symptoms vary according to the part of your body affected, but 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.

What causes allergies?

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

What are the common allergens?

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 are not common. Most reactions to food are more likely to be food intolerance, which doesn’t involve your body’s immune system. An allergic reaction involves your body's immune system. Read more about the difference between food allergies and food intolerance.

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

What are the types of allergic conditions?

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

What are the symptoms of an allergic reaction?

Symptoms depend on where allergens enter your body and which part of your body is affected. They can range from mild to severe. Typically, symptoms happens within minutes to an hour after you are exposed to a particular allergen.

  • Hay fever (also known as  allergic rhinitis) 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 a condition 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. Read more about anaphylaxis.

How are allergies diagnosed?

It's important to talk to your doctor if you think you or your child may have an allergy to something. There are many causes of allergies and some symptoms may be due to other conditions.

Your GP or doctor will ask you or your child about allergic symptoms such as a rash or an upset stomach. Other questions may include the following:

  • When do your symptoms occur when exposed to a particular allergen?
  • How often do your symptoms occur?
  • Is there anything that will trigger your symptoms?
  • Are there any family members who also have allergies?
  • Have you been exposed to new foods, pets or medicines recently?

When symptoms appear soon after you have been exposed to a particular allergen, it is easy to identify which allergen is causing your reaction. However, if the cause is unknown, other diagnostic tests may be needed. 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 doctor may also refer you or your child to a paediatric clinic or allergy specialist for further tests if the cause is still unclear.

Skin prick tests

  • A needle is pricked into your skin through a drop of the suspected allergen, usually on the skin of your inner forearm or back.
  • The size of the weal on your skin indicates how strongly you are allergic to a particular allergen.
  • As many as 30 allergens can be tested at the same time to work out the particular substances you are allergic to.

How are allergies treated?

Treatment depends on the type of allergies you have. Find out more about treatment and how to care for yourself when you have allergies.

How can I prevent 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 more about ways to prevent an allergic reaction.

What support is available with allergies?

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

Learn more

The following links provide further information about allergies. Be aware that websites from other countries may have information that differs from New Zealand recommendations.   

A–Z allergies Allergy NZ
Allergy FAQs  Allergy NZ
Allergies Ministry of Health, NZ
Allergy KidsHealth NZ
Allergies HealthInfo Canterbury, NZ
What is allergy? The Australasian Society of Clinical Immunology & Allergy
Allergies NHS, UK
Allergies PatientInfo, UK
Allergies factsheet in multiple languages Health Information Translations

References

  1. Allergies Auckland Regional HealthPathways, NZ, 2020
  2. Calderon MA, Alves B, Jacobson M, Hurwitz B, Sheikh A, Durham S. Allergen injection immunotherapy for seasonal allergic rhinitis Cochrane Database of Systematic Reviews 2007. Issue 1. Art. No.: CD001936. DOI: 10.1002/14651858.CD001936.pub2.
  3. Assessing the efficacy of immunotherapy for desensitisation of peanut allergy in children The Lancet, Volume 383, Issue 9925, Pages 1297–1304, 12 April 2014.
  4. Personal action plans for allergies Australasian Society of Clinical Immunology and Allergy (ASCIA)
Credits: Health Navigator Editorial Team.