Food Allergy vs Food Intolerance

An allergy happens when a person's immune system treats a substance (allergen) like an inappropriate invader, releasing a chemical called histamine that causes the unpleasant, sometimes dangerous, symptoms of a reaction — which can start very suddenly, even after exposure to a small amount. Allergens can enter the body inhaled (dust, pollen), ingested as food (nuts, eggs, shellfish are common ones) or medication (like penicillin), injected by an insect sting, or absorbed through the skin (like poison ivy).

Food intolerance is different

Food intolerance is not caused by an immune reaction. It causes discomfort but is not dangerous to your child — you may notice bloating, loose stools, gas or other symptoms after a specific food. Even though it's not dangerous, if it causes discomfort you may want to avoid that food in the future.

Lactose intolerance

Lactose intolerance happens when the body doesn't produce enough of the enzyme lactase to fully break down lactose, the sugar in most dairy products. It's rare in young children and usually only develops after age 3. If your child is lactose intolerant, you can give her the calcium she needs with lactose-free or lactose-reduced milk, along with fortified soy milk, yoghurt, canned salmon or sardines with edible bones, oranges or fortified orange juice, broccoli, almonds and pinto beans — though none of these alone provides enough calcium, and many don't provide enough vitamin D either, so ask your doctor about a supplement.

Preventing allergies — what the evidence actually says

There's no evidence that avoiding certain foods will prevent allergy in your child. There's no evidence that soy-based formula prevents your child from developing an allergy. And it isn't recommended that you delay introducing a food beyond 6 months of age to try to prevent an allergy — this applies even to children considered at high risk (with a parent or sibling who has an allergic condition). You don't need to avoid milk, egg, peanut or other foods while breastfeeding, either. Once you do offer common allergens, it's important to keep offering them regularly, and to speak to your health care provider if you have concerns.

How will I know if my child has a food allergy?

Most often, a child has to eat a food more than once before you know he's allergic — the first exposure to nuts, for example, will probably show no reaction, but if an allergy develops, the next exposure could be more serious. Signs of an allergic reaction can include an itchy mouth and throat, hives, stomach trouble (diarrhoea, cramps, nausea, vomiting), swelling of the face or tongue, or trouble breathing.

What is anaphylaxis?

In rare cases, a child may have a rapid, severe reaction called anaphylactic shock or anaphylaxis, which can happen within minutes or up to 2 hours of exposure. Symptoms include difficulty breathing; swelling of the face, throat, lips or tongue; a rapid drop in blood pressure; dizziness; unconsciousness; hives; tightness of the throat; a hoarse voice; and light-headedness. If any of these happen, go to the nearest emergency department or call an ambulance immediately.

Common allergens

Any food can trigger an allergic reaction, but the most common are peanuts, tree nuts, eggs, shellfish, fish, milk, soy and wheat. It's hard to diagnose food allergies — if your child reacts to a food, your doctor will refer you to an allergist for proper testing, and if an allergy is confirmed, may prescribe an epinephrine auto-injector (such as an EpiPen or Allerject) to protect your child right away if exposed again.

Do children outgrow food allergies?

Many children outgrow food allergies, especially ones that started before age 3 — allergies to milk, for example, usually go away. Others, like allergies to nuts and fish, probably won't.