Allergy

Allergy

Allergies happen when your child's immune system mistakenly treats normally harmless substances as 'harmful'. The substances that trigger allergies are called allergens. The symptoms of an allergy vary according to what a child or young person is allergic to. 

Key points to remember about allergy

  • allergies happen when your child's immune system mistakenly treats normally harmless substances as 'harmful'
  • the substances causing allergies are called allergens
  • the immune system then releases histamine and other chemicals that cause symptoms
  • environmental/airborne allergens (such as house dust mites, pollen, pets) can cause 'hayfever' (allergic rhinitis) - sneezing, itchy eyes and a runny or blocked nose
  • food allergy (and also bee or wasp stings, latex, medicines) can cause mild reactions such as hives and itching, to severe symptoms called anaphylaxis
  • anaphylaxis is a life-threatening  allergic reaction which needs urgent medical treatment

What is an allergy?

Allergies happen when your child's immune system mistakenly treats normally harmless substances as 'harmful'. The substances that trigger allergies are called allergens. Your child's immune system overreacts to the allergen by making allergic antibodies (IgE) against the allergen. The immune system then releases histamine and other chemicals that cause symptoms.

There are many types of allergens found in our environment. The most common of these are:

  • airborne allergens that come from dust mites, cats and dogs, pollen, moulds
  • food allergens
  • insect stings
  • other things such as medicines or latex

Once your immune system has made IgE against an allergen, coming into contact with that allergen can result in an allergic reaction, with symptoms that can range from annoying to life-threatening.

Who gets allergies?

It's not clear exactly why some people have allergies and others don't. 

The tendency to develop allergies is usually passed down through your genes. But, not everybody in a family will have the allergies. Members of the same family may have allergies to different things and some people may develop allergies when no other member of the family has any. When a child is allergic to one thing, it is likely that they may be allergic to other substances as well. 

As well as family history, many factors in the environment may have an impact. 

What are the signs and symptoms of allergies?

The symptoms of an allergy vary according to what a child or young person is allergic to.

Airborne allergens such as pollen usually cause 'hay fever' (allergic rhinitis). Children with 'hay fever' may have seasonal symptoms with a runny, itchy nose or eyes and sneezing during grass pollen season. Children who are allergic to dust mites may have year-round 'hay fever', with a runny or blocked nose and sneezing, often worst in bed. Airborne allergens can also contribute to the symptoms of asthma and eczema.

Children with food allergies get symptoms most often on eating the food that they are allergic to. Symptoms of food allergy can include skin rashes (such as hives or welts), swelling of the face, lips and eyes, and tummy pains, vomiting and diarrhoea. Some children may have a severe reaction with breathing problems (for example, cough and wheeze) or collapse. This is called anaphylaxis and can be life-threatening.

If your child is allergic to a food, touching that food is very unlikely to cause a severe allergic reaction. Some skin rashes may appear on the part of the skin the food has touched. 

Being in the same room as the food is also very unlikely to cause a reaction. But, cooking vapours from some foods, such as egg or fish, may trigger a reaction in some people.

How are allergies diagnosed?

Your doctor usually diagnoses allergies once they have listened to your story and examined your child.

Environmental allergies may be obvious from your child's story (for example, your child gets itchy and sneezy every time they pat a cat). But sometimes, your child might need testing for these allergies.

If food allergy is suspected, your child may need an allergy test (skin tests or a blood test for specific allergic antibodies, previously called a RAST) to confirm what they are allergic to. This is to make sure you know what foods your child needs to avoid. In some cases, your child might need to go to a paediatric clinic or specialist.

In babies and young children, some food allergies are not caused by IgE antibodies. These food allergies are known as 'non-IgE-mediated food allergies'. These types of allergies can take a long time to diagnose and you will often need the help of a paediatrician or specialist and dietitian.

What are the most common airborne allergens?

Some of the most common things people are allergic to are carried through the air. These include:

How do I manage my child's food allergies?

Avoiding the allergen

Once your family doctor, paediatrician or specialist diagnoses your child's food allergy, managing it includes avoiding the allergen. Make sure your child also avoids all the different products containing the allergen and the different forms it might come in. Families often need help from a dietitian to do this. See the ASCIA website for information about food allergy, including general avoidance measures for the most common food allergens. Allergy New Zealand has a food allergen labelling guide

Allergic reaction or anaphylaxis action plan

All children with food and insect sting allergy need to have an allergic reaction or anaphylaxis action plan explaining how to manage an allergic reaction. (See the section on anaphylaxis below). Children with food allergy need follow up to see whether their food allergies are going away. ASCIA (the Australasian Society of Clinical Immunology and Allergy) has developed several action plans for use in Australia and New Zealand.

See the various action plans at the ASCIA website.

'Non-IgE-mediated' food allergy

Some young children have different types of food allergy called 'non-IgE-mediated' food allergy. These conditions can be harder to identify and are more common in babies and very young children.

Food allergy and asthma

Some children with food allergy also have asthma. It is important they have asthma medicines and an asthma management plan to keep their asthma under control. Having asthma can make an allergic reaction to food more severe. If your child is using their reliever inhaler more than a couple of times a week, or they are more breathless, wakeful at night or coughing more, you should see your doctor.

Avoidance of airborne allergies is sometimes possible - see advice about this on the ASCIA website. You can use medicines such as nasal sprays and antihistamines to treat allergic rhinitis/hay fever.

What are the most common food allergens?

These include:

  • milk (dairy)
  • eggs
  • tree nuts and peanuts
  • fish and shellfish
  • sesame
  • soy
  • wheat

Almost any food can trigger an allergy in some children and young people. 

What are other common allergens?

These include:

  • insect stings (bees and wasps)
  • medicines
  • latex

What is anaphylaxis?

Anaphylaxis can be life-threatening - it's an emergency which needs immediate treatment.

Anaphylaxis is the most severe form of allergic reaction and can be life-threatening. Anaphylaxis is an emergency that needs immediate treatment with an injection of a medicine called adrenaline (epinephrine). This is the medicine in automatic injectors such as the EpiPen®. The child or young person needs to sit down - they must not stand or walk. Phone 111 within New Zealand for an ambulance (use the appropriate emergency number in other countries). 

What are the signs and symptoms of anaphylaxis?

The signs and symptoms of anaphylaxis include:

  • difficulty breathing/noisy breathing
  • swelling of the tongue
  • swelling/tightness in the throat
  • difficulty talking and/or a hoarse voice
  • wheeze or persistent cough
  • dizziness or lightheadedness
  • loss of consciousness and/or collapse
  • being pale and floppy (in young children)
  • tummy pain or vomiting in children with insect allergy

How long does it take for anaphylaxis symptoms to occur?

The symptoms can occur within seconds of coming into contact with the allergen or can take up to 2 hours to occur.

Can there be any warning signs before anaphylaxis?

In some cases, less dangerous allergic symptoms appear before anaphylaxis. These include:

  • swelling of the face, lips and eyes
  • hives or welts on the skin
  • tummy pain, vomiting
  • a feeling of 'doom' or a young child becoming quiet or clingy

What influences how severe anaphylaxis is?

Several things can influence how severe anaphylaxis is, including:

  • exercise
  • heat
  • in food-allergic people, the amount of allergen they have eaten and how the food was prepared
  • not enough sleep
  • having alcohol or drugs 

Severe allergic reactions require urgent medical attention.

This page last reviewed 13 December 2019.
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