What is an allergy?

The immune system protects us by attacking harmful substances such as viruses and bacteria. An allergy is the immune system’s response to a substance called an allergen.

The allergen is not harmful for most people. However, when a child has an allergy, the immune system treats the allergen as an invader and over-reacts to it. This results in symptoms from mild discomfort to severe distress.

Allergic disorders, including food allergies, are common in childhood. Many children with allergies also have asthma.

What causes an allergic reaction?

Allergens may come in contact with the skin or be breathed in, eaten or injected.

When the body detects an allergen, it sends a signal to the immune system to produce antibodies called immunoglobulin E (IgE). Those antibodies cause certain cells in the body to release chemicals called histamines. Histamines travel through the bloodstream to fight the invading substance or allergen.

Your child’s allergic reaction depends on which part of their body has been exposed to the allergen. Most commonly, allergic reactions affect the eyes, inside of the nose, throat, lungs or skin.

Types of allergens

Common airborne allergens

Get Adobe Flash player

Dust mites are common airborne allergens. These tiny bugs live in warm, damp, dusty places in your home and survive by eating dead skin cells. Their waste is a major cause of allergies and asthma.

Other common airborne allergens include:

  • pollen from flowers and other plants
  • mould
  • pet dander (dead skin cells from pets)
  • cockroaches.

Common food allergens

The most common food allergens include:

Get Adobe Flash player

Even small amounts of these foods can trigger anaphylaxis in some allergic children. Anaphylaxis is the most severe type of allergic reaction.

Food allergens can also be hidden in common party dishes such as cookies, cakes, candies or other foods. Always ask the cook or the host if dishes contain foods your child is allergic to.

Far more people have a food intolerance than a food allergy. Unlike a food allergy, a food intolerance does not involve an immune reaction. Rather, it produces unpleasant symptoms as food is digested. These symtpms appear over a few hours rather than as soon as the food is swallowed or inhaled.

Other common allergens

  • Insect stings
  • Medicines

Signs and symptoms of allergies

Allergic reactions will vary from child to child and from allergen to allergen. Where you live can also affect the type and severity of the allergy.

Common allergy symptoms may include:

  • breathing problems
  • burning, tearing or itchy eyes
  • conjunctivitis (red, swollen eyes)
  • coughing
  • hives (raised, red, itchy bumps)
  • runny nose
  • skin rashes
  • wheezing
  • swelling around the face or throat
  • shock.

Symptoms for airborne allergens

Airborne allergens usually cause sneezing, itchy nose or throat, nasal congestion, red and itchy eyes and coughing. Some children also have wheezing and shortness of breath.

Symptoms for food allergens and insect bites

Your child’s response to a food allergy or insect bite will depend on how sensitive they are to that food or bug. Symptoms can include:

  • itchy mouth and throat when food is swallowed
  • hives
  • vomiting
  • diarrhea
  • runny, itchy nose
  • difficulty breathing
  • swelling around the face or throat
  • going into shock.

What your child's doctor can do for allergies

If you suspect your child has an allergy, consult an allergist. This is a doctor who specializes in diagnosing and treating allergies.

To identify your child's allergy, the allergist will usually:

  • examine your child
  • ask for your child’s allergy history
  • ask for a description of your child’s allergic symptoms.

Your child might then have skin tests, blood tests, a chest X-ray, a lung function test or an exercise tolerance test. The doctor will explain these tests to you.

When the tests are done, the allergist will use the results to make a diagnosis. You and your child will meet the allergist at a later date to discuss them.

How to prepare for an allergy test

Your child may need to stop using certain medications for a period of time before an allergy test. These medications may include antihistamines and other pills for motion sickness. Always ask your doctor if your child should stop taking medications before the visit.

Taking care of your child with an allergy at home

If your child has a severe allergy, your doctor might give you a prescription for an epinephrine auto-injector (Epi-Pen or Allerject). Your doctor can show you how and when to use the auto-injector. You or your child may need to carry one at all times.

As much as possible, try to prevent allergic reactions by reducing your child's contact with the allergen(s). The steps you take depend on the substance to which your child is allergic. Discuss this with your child's doctor.

How to prevent allergic reactions

Airborne allergens

  • Have a pet-free home. Or if you have a pet, keep it out of the child’s room and bathe it regularly.
  • Remove carpets and rugs from the home, especially from your child’s bedroom. Hard floor surfaces do not collect dust as much as carpets do.
  • Reduce the relative humidity in the home.
  • Wash bedding in hot water. This will help reduce dust mites.
  • Control contact with outdoor pollen by closing windows in peak seasons. Use an air conditioning system with a small-particle filter.
  • Get rid of items in the home that collect dust. These include heavy drapes or old, unclean furniture.
  • Clean your home often.
  • Seal pillows and mattresses if your child is allergic to dust mites.
  • Keep bathrooms and other mould-prone areas clean and dry.

Food allergens

Your child must avoid all foods they are allergic to. Some children may outgrow their allergies, but others may have to avoid the allergen for life.

Avoiding a food allergen can be difficult. As a result, many children unintentionally eat food they are allergic to.

If your child has a food allergy, teach them to be aware of the foods to avoid and all the possible names of those foods. You and your child should learn to read labels on food packaging and ask questions about served food. Your child should also know why it is important to look for an allergen in ingredients.

It is also important to tell all caregivers about your child’s allergy and any foods or drinks your child must avoid.

When to get medical help for an allergic reaction

Call 911 or take your child to the nearest emergency department if they have:

  • breathing difficulties
  • swelling, particularly of the face, throat, lips or tongue
  • a rapid drop in blood pressure
  • dizziness
  • loss of consciousness
  • hives
  • tightness of the throat
  • hoarse voice
  • lightheadedness.

Your child should also go to the nearest emergency department even if they have received epinephrine (EpiPen or Allerject), as the symptoms can start again hours after the epinephrine is given.

Key points

  • An allergy is the immune system’s response to a substance that is not harmful to most people.
  • If you suspect that your child has an allergy, an allergist can do tests to find out exactly what is causing the allergy and the severity of your child’s reaction.
  • To reduce your child’s exposure to airborne allergens, have a pet-free home and remove carpeting.
  • To manage a food allergy, make sure your child avoids all foods they are allergic to and learns how to read food labels and ask about the ingredients in served food.
  • If your child has a severe allergy, tell their teachers and other caregivers.


Anna Kasprzak, RN​