I think my child has outgrown their food allergy. How can I be sure?

Some children grow out of their food allergies, but researchers don’t exactly know why.

Here’s how to work with your allergy specialist if you suspect your child isn’t allergic any more.

Read more: Four myths about allergies you thought were true – but aren't

Who’s more likely to grow out of their food allergy?

Food allergy affects up to 10% of infants and 8% of children in Australia and New Zealand. Common food allergies in young children are egg, cow’s milk and peanut. Allergies to tree nuts, fish and seafood tend to be more common in adolescents.

Rates of food allergies have increased in children and adults in developed countries including Australia. There’s also an increase in the number of children up to four years old who’ve been admitted to hospital with food anaphylaxis (a severe, life-threatening reaction).

Read more: Introduce eggs and peanuts early in infants' diets to reduce the risk of allergies

Yet, Australian research shows almost all children (more than 80%) with an egg allergy outgrow their allergy by the time they are four years old, as do about 20% of children with a peanut allergy.

However, for others, food allergies are likely to persist. This is most likely if they have eczema, hay fever and/or asthma alongside a tree nut allergy from a young age, or they have a severe allergic reaction to a low dose of their particular food allergen.

Why do they outgrow their food allergy?

Researchers don’t know exactly why some children grow out of their food allergies. But their immune response to food allergens seems to change.

For instance, these children have lower levels of antibodies you’d normally see as part of an allergic response (lower levels of allergen-specific IgE). They also have higher levels of other immune system components (allergen-specific IgG4, IL-10 and allergen-specific T cells).

Other research has focused on a type of T cell, called the regulatory T cell, which regulates how the adaptive immune system responds to antigens.

Children who are not allergic or have developed naturally occurring tolerance are more likely to have stable levels of these cells. However, children with an allergy may not be able to regenerate these cells once exposed to the food allergen, so have lower levels.

Read more: Explainer: what is the immune system?

Children who outgrow their food allergies may also have a dampened inflammatory response in a part of their immune system known as the innate immune system.

Lastly, changes in the diversity of gut microbiota (microorganisms such as bacteria living in the gut) and substances made by these microbes may also be involved.

However, we need more research to verify what’s happening both in the immune system and the gut microbiome to be sure.

Read more: Essays on health: microbes aren't the enemy, they're a big part of who we are

What signs can parents look out for?

If you think your child has outgrown their food allergy, it’s important not to test them yourself to see what happens. This is extremely unsafe and they may have a severe allergic reaction.

However, you may have noticed your child has accidentally eaten a food allergen but did not develop an allergic reaction. This may indicate your child has outgrown the food allergy.

That’s when it’s time to consult an allergy specialist – a doctor who specialises in diagnosing and managing patients with allergic diseases – to investigate.

Here’s what an allergy specialist will do

The allergy specialist will conduct a number of tests to monitor your child, either annually or every few years, depending on the allergen. These tests include skin prick tests and blood tests.

These tests indicate changes in the immune system to give us an idea of whether your child has outgrown an allergy or it persists.

Read more: Early exposure to infections doesn't protect against allergies, but getting into nature might

When these tests indicate almost no allergic response, your child will have an oral food challenge under medical supervision.

For example, a child will be given the food allergen in increasing amounts in a medical facility. If the child tolerates the food (known as passing the challenge), the food is regularly reintroduced into the diet.

Food challenge tests are also done to see if a child can tolerate foods in a modified form. For example, a child allergic to eggs or cow’s milk may be able to tolerate baked egg or baked milk.

In general, it’s only with a medically supervised oral food challenge that allergy specialists can say whether your child has really outgrown their food allergy.

If your child has a food allergy, more information is available from Allergy & Anaphylaxis Australia and the Australasian Society of Clinical Immunology and Allergy. You can also listen to the Allergies podcast, by Murdoch Children’s Research Institute’s specialists Professors Katie Allen and Mimi Tang.