Allergic reactions and allergy tests factsheet

Introduction

The immune system is the part of the body that keeps you healthy by fighting infection and germs. The immune system makes proteins called antibodies that stick to and attack germs.

The immune system has a memory and can quickly find and fight germs it has previously been exposed to.

Sometimes, the immune system learns to react to something that is not usually harmful, like:

  • pollen
  • some foods
  • animal dander – flakes of skin, fur, hair, or feathers
  • insect stings. 

When this happens, it is called an allergic reaction or having an allergy.

Substances that are not usually harmful but can cause a reaction are called allergens.

Allergic reactions can range from mild to life-threatening. It is important to have allergies tested and managed by a doctor.

 Signs and symptoms

Allergic reactions usually happen 5-30 minutes after exposure to an allergen but can take up to two hours.

Mild to moderate symptoms of allergic reaction can include:

  • swelling of the lips, face, or eyes
  • hives or welts on the skin
  • a tingling feeling in the mouth
  • abdominal pain- also signs of a severe reaction to insect stings.

Some children can have a more severe allergic reaction called anaphylaxis.

Signs of anaphylaxis include: 

  • wheezing, difficult, or noisy breathing 
  • swelling of the tongue
  • swelling or tightness in the throat
  • a persistent cough
  • difficulty talking or a hoarse voice
  • dizziness
  • becoming pale and floppy in young children
  • collapsing.

If your child has signs of anaphylaxis, you should:

  • follow your child’s ASCIA action plan for anaphylaxis if you have one
  • use an EpiPen® or Anapen®, if available
  • call Triple Zero (000) for an ambulance.

Diagnosis

If you think your child has had an allergic reaction that is not anaphylaxis, write down the following and see your local doctor as soon as possible:

  • time of exposure
  • the allergen
  • time of reaction
  • type of reaction.

A specialist doctor can diagnose allergies based on your child’s:

  • medical history
  • signs and symptoms
  • results from allergy tests.

Skin prick test

A skin prick test is a common type of allergy test.

The nurse will let you know whether there are any medications your child should avoid for three days before the test. This is to make sure nothing interferes with the results.

In a skin prick test:

  1. the nurse or doctor will write numbers on the skin to show where an allergen will be tested
  2. the nurse or doctor will then drop a tiny bit of the allergen into the skin and then prick the skin with a small needle called a lancet
  3. the process is repeated depending on how many allergens are tested.

After 15 – 20 minutes, a red lump or welt will appear on the skin where there is an allergic reaction.

Skin prick testing can make children uncomfortable as the reactions can feel itchy for a short time afterwards.

Some allergens need a different type of skin test called intradermal skin testing. Intradermal skin testing is used for allergens that have a higher risk of anaphylaxis, including:

  • medications like penicillin
  • vaccines
  • animal or insect venom.

Intradermal skin testing is done in the hospital by a specialist doctor.

Do not try skin testing at home.

Blood test

Blood tests check for higher levels of allergy antibodies in the blood. 

Blood tests are used when:

  • a skin test is not available
  • a child cannot have a skin test due to conditions like eczema
  • a child is taking medications that interfere with skin test results, like antihistamines.

Food challenge

A food challenge confirms whether a child has a food allergy or has grown out of it. It is usually done in the hospital under medical supervision.

Skin patch testing

Patch testing is used to see whether your child has an allergic reaction on the skin called contact dermatitis. 

Things that can cause contact dermatitis include:

  • tape and bandages
  • plants
  • cosmetics like make-up or beauty creams
  • metals like nickel found in jewellery.

In a patch test, your child will have a patch with an allergen in it applied to their back. After 48 hours, the doctor will remove the patch and check the skin for a reaction.

Tests that do not diagnose allergy

Many other tests are advertised as allergy tests. However, these tests cannot diagnose allergies and do not have any scientific evidence to support them.

These tests can include:

  • cytotoxic food testing
  • applied kinesiology
  • electrodermal testing
  • pulse testing
  • reflexology
  • hair analysis.

Results from these tests might lead to incorrect treatment or information. 

Always speak to your child’s doctor if you have any questions or concerns about allergy tests and information.

Benefits of allergy testing

Allergies can have a big impact on your child’s everyday life. It is important to have your child tested and treated if you think they have an allergy.

Benefits of allergy testing include:

  • getting support and information about allergies and preventing reactions
  • knowing whether your child’s allergy is life-threatening or not
  • knowing how to avoid certain foods and products.

If the test shows that your child does not have an allergy, it may mean that another health issue needs to be investigated.

Treatment

Your child's doctor will find the best possible treatment for their allergy based on their individual health needs. In most cases, your child will need to avoid their allergen carefully. 

Your child’s doctor will develop an ASCIA Action plan to share with anyone who cares for your child, including parents, carers, childcare and schools. ASCIA Action plans are used to manage allergies and allergic reactions safely.

Children at risk of anaphylaxis will also need an adrenaline autoinjector, also known as an EpiPen® or Anapen®.

 Management

Intolerances

Some children will experience food intolerances, which can be mistaken for allergies due to similar symptoms. 

Allergies and intolerances are different. 

  • Allergies affect the immune system 
  • Intolerances affect the digestive system

A common intolerance is lactose, the sugar found in dairy products.

Food intolerances do not cause anaphylaxis. If you are concerned about food intolerances in your child, speak to your local doctor.

Atopy

Atopy is the word for people more likely to develop an allergy. Atopy can be passed down in families and can cause conditions like:

Allergic rhinitis (hay fever)

Allergic rhinitis is also known as hay fever. Hay fever is a very common allergy that happens when you breathe in allergens like:

  • pollen
  • mould
  • dust mites
  • animal dander - fur, hair, or feathers.

Hay fever can happen year-round and might worsen in some states and territories around spring and summer.

Hay fever can look like a common cold, with symptoms including:

  • runny nose
  • blocked nose
  • watery eyes
  • itchy eyes
  • wheezing
  • coughing
  • sneezing.

Eczema

Eczema is also known as atopic dermatitis. An allergy does not commonly cause eczema, but children with eczema can have allergies that cause similar symptoms or make eczema worse.

Eczema is slow to develop and cannot be diagnosed with a skin prick test.

Adverse reactions

Adverse reactions are unwanted or harmful effects that happen after eating, inhaling, injecting, or touching something.

Adverse reactions are different to allergies and can include:

  • food intolerance - a chemical reaction in the body to a food or drink
    • sweating
    • headaches
    • diarrhoea - loose, watery poo
    • feeling of tightness.
  • food poisoning – sickness from ingesting food contaminated with bacteria, parasites and other germs
  • enzyme deficiencies – genetic disorders that stop the body from processing some foods properly
  • food aversion – a strong dislike or refusal to eat certain foods.

These reactions can be confused with allergies and should be checked by a doctor.

Toxic reactions from ingesting poison, like chemicals or plants, are different from allergies but are severe and can cause death. If your child has ingested a poison, call Triple Zero (000) for an ambulance or go to the nearest emergency department.

Last updated Wednesday 12th June 2024

Disclaimer

This factsheet is provided for general information only. It does not constitute health advice and should not be used to diagnose or treat any health condition.

Please consult with your doctor or other health professional to make sure this information is right for you and/or your child.

The Sydney Children’s Hospitals Network does not accept responsibility for inaccuracies or omissions, the interpretation of the information, or for success or appropriateness of any treatment described in the factsheet.

© Sydney Children’s Hospitals Network 2024


This factsheet was produced with support from John Hunter Children's Hospital.