Allergy

Allergy

Allergies happen when your child's infection-fighting system has made an allergic response to a substance (called an allergen).

Key points to remember

  • allergies happen when your child's infection-fighting (immune) system has made an allergic response to a substance (called an allergen)
  • when there is repeated contact with that allergen your child may experience symptoms
  • symptoms of allergy range from mild and annoying to severe and potentially life threatening
  • anaphylaxis is a life threatening allergic reaction which requires urgent medical treatment 

What is an allergy?

An allergy occurs when a person's infection-fighting (immune) system reacts to substances (allergens) in the environment by making allergic antibodies (IgE) against the allergens.  Most allergens do not cause problems for most people. 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 venom
  • other things such as drugs or latex

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

Who gets allergies?

The tendency to develop allergies is usually passed down through your genes. However, 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.

What are the signs and symptoms of allergies?

The symptoms of an allergy vary according to what a 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 gastrointestinal symptoms such as stomach pains, vomiting and diarrhoea. Some children may have a severe reaction with breathing problems (for example, cough and wheeze) or collapse.

How are allergies diagnosed?

Allergies are usually diagnosed once your doctor has listened to your story and examined your child.

Food allergies need to be confirmed by allergy tests (skin tests or a blood test for specific allergic antibodies, previously called a RAST). This is to make sure you know what foods need to be avoided. 

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 these allergies will also need to be evaluated by testing.

How are allergies managed?

Once the diagnosis of a food allergy is confirmed, treatment includes avoiding the allergen. Families often need help from a dietitian to do this. All children with food allergy need to have a management plan explaining how to manage an allergic reaction on accidental food exposure.  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.

Avoidance of airborne allergies is sometimes possible, with advice about this also on the ASCIA website. Medications may be used to treat allergic rhinitis/hay fever.

What are the most common airborne allergens?

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

  • dust mites which live in carpets, bedding and upholstery
  • pollens from trees, grasses and other plants
  • animals such as cats, dogs and horses
  • moulds, which thrive in warm, dark, moist places, such as bathrooms, basements and outdoors in compost heaps

Common food allergens

These include:

  • dairy products such as cow's milk and milk products such as butter and yoghurt
  • eggs
  • nuts and peanuts
  • fish and shellfish
  • soy
  • wheat (which is found in breads and cereals)

Other common allergens

These include:

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

What is anaphylaxis?

Anaphylaxis is the most severe form of allergic reaction and can be life-threatening. Anaphylaxis is a medical emergency which needs immediate treatment.

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 light headedness
  • loss of consciousness and/or collapse
  • being pale and floppy (in young children)

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

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
  • stomach pain, vomiting

Several factors can influence the severity of anaphylaxis, including exercise, heat and in food allergic people, the amount of allergen eaten and how it is prepared.

Severe allergic reactions require urgent medical attention.

This page last reviewed 24 June 2015.
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