Food allergies can be difficult to identify, but left untreated they can sometimes be serious. We asked leading paediatric allergist Professor George Du Toit how to spot the signs of an allergy in children, what types of food allergy children grow out of, and what allergies need treatment.
Young children are just as prone to allergies as anyone else, and can be affected by a range of conditions – including food allergy, eczema, hay fever, and asthma. However, we must not overlook the way that these conditions can interact, with food allergy sometimes being a factor behind the development of eczema.
In the case of early onset eczema that is severe, we frequently find food allergy. There's a very close association between food allergy and eczema, with food allergy exacerbating the eczema and paradoxically, often the eczema causing the food allergy.
How do I know what food my child is allergic to?
Sometimes it can be difficult to find out what exactly is giving your child an allergic reaction, and sometimes it is very clear.
The gold standard of course is to eat the food.
Some symptoms are unequivocal signs of an intolerance. For example, if you ate some peanut and you develop immediate onset swelling, hives, vomiting, cough and wheezing, you're peanut allergic.
If on the other hand you’ve tried eating something and have no reaction, this is strong evidence you are tolerant of it.
When you go to see an allergist they will take down a detail history of what you’ve tried and what symptoms you experienced. A single event of unequivocal symptoms, like the one described above, is strong evidence of an intolerance. If it has happened on two or three occasions, the diagnosis is even more secure.
However, if you haven’t tried eating the food on its own, if the symptoms are more equivocal, or if there are other risk factors that could explain the testing, then the doctor would likely recommend testing:
- A skin prick test is where drop of the allergen is placed on the arm and a Lancet is used to lightly touch through this and to look for a hive that may result.
- A blood test can also be performed and this measures the IgE antibody: the allergy antibody
Both are highly accurate when the test results are high – and of course, when they are negative. So, the negative predictive value, the chance that you will not react to the food if your test is negative is extremely high. The positive predictive value, in other words, the chance that you do have the allergy if the test result is high on skin prick test or IgE, again, is also high.
Where a diagnosis is uncertain, we then rely on an oral supervised food challenge test. So here we would provide increments of the food in a safe and supervised setting and look for symptoms. And of course, if an age appropriate amount of the food is eaten with no symptoms that child is peanut tolerant.
Finally, you must be cautious of tests such as IgG4 tests. These are not accurate tests for food allergy.
Will my child outgrow their allergy?
It depends on what they are allergic to. For example, milk and eggs are considered childhood allergies as very few children will carry this into this second and third decades of life. Indeed, young infants with egg and milk allergy enjoy a very good prognosis – typically after three or four or five years, they'll start safety ingesting baked milk products, because the heating damages the allergen, and in a year or two later after that they'll tolerate just regular milk and egg based products. Wheat is commonly outgrown as are soy and some other allergies.
Certain allergies are generally not outgrown; they are only outgrown in ten to fifteen percent of children. These include:
- fish allergy
- shellfish allergy
- peanut allergy
- tree nut allergies such as cashew and pistachio
- walnut allergy
- sesame allergy
Families often ask about active programmes to treat these allergies.
How is food allergy treated?
Treatment for food allergy is complex. We are currently researching this and there are various modalities, such as patches applied to the skin and small measured oral increments of these in a safe and supervised setting.
However, these currently remain in the research setting and should not be applied at home. These are not home remedies, as remember you'll be feeding the allergen to an allergic patient and that can induce severe reactions.