Every parent knows well the struggles of getting tots to try new foods. But what if you find out that one of them sends your child’s immune system into revolt?

Rebecca Montemurro, 34, recalls how her son, Theo, now 4, would instantly vomit after breastfeeding if she had eaten dairy prior to or during a feeding. “I finally put two and two together after about three months, so I cut out dairy,” remembers the Hamilton, Ont., mom. They tried reintroducing dairy when Theo turned one, but symptoms returned with a vengeance. At 16 months, their pediatrician finally referred Theo to an allergist, where he tested positive for milk protein allergy. “We probably should have gone sooner since my motherly senses knew something wasn’t right. We had already taken the precautions and omitted dairy well before they had told us to.”

“There are about 170 foods that have been known to cause an allergic reaction and nine of them are responsible for about 90 percent of allergic reactions,” says Laurie Harada, executive director of Anaphylaxis Canada. The nine most common food allergy sources listed by Health Canada are: peanuts, tree nuts, sesame seeds, milk, eggs, seafood (fish, crustaceans and shellfish), soy, wheat and sulphites (a food additive).

when food allergies first appear

“Food allergies in children tend to develop within the first year of life and milk and egg are common allergies from birth to age two,” says Dr. Wade Watson, professor of pediatrics at Dalhousie University and head of the Division of Allergy at the IWK Health Centre in Halifax. Many of those children will outgrow their allergy by the time they go to school, says Dr. Watson. About 20 percent will outgrow a peanut allergy between the ages of about 5″“15. Although food allergies most often appear in infants and children, they can appear at any age. Your child may also have a greater potential for food allergies if he has or has had severe eczema, cough/wheezing with colds, or if there’s a strong family history of allergies (asthma, rhinitis/hay fever, or food).

early warning signs

Typical signs of an allergic reaction include swelling of throat, lips or face, hives or vomiting. Anaphylaxis, which involves breathing problems or a drop in blood pressure, is a severe reaction which can be life-threatening. So what does it take to cause a reaction? In the case of some allergens such as peanuts, swallowing an unsuspected trace amount can be enough to set off the alarm system in your child’s body. Basically, the smaller the amount of a food it takes to provoke symptoms, the more severe the food allergy may be. “If you notice a reaction, stop giving your child the suspected food, start keeping a food diary and see your child’s doctor for an allergist referral,” advises Harada.

Antihistamines may work well for allergy symptoms such as hives, but inside swelling (lips, mouth, tongue), vomiting or breathing difficulties will need more urgent treatment with an EpiPen (epinephrine auto injector). “There’s no such thing as a “mild’ food allergy. If your child has one, you need to exercise proper caution,” says Dr. Watson. Talk to a doctor about whether an EpiPen is necessary, as well as how and when to administer it.

time to test for allergies

“If a child has had any kind of immediate reaction, such as gastrointestinal symptoms or hives, get her assessed by an allergist. What we don’t want is people avoiding foods they only think children are allergic to,” says Dr. Watson. He adds, “Skin tests do not by themselves make a diagnosis of a food allergy. The history is very important.” Sometimes, parents may suspect that their children are allergic to A, B and C, but testing may prove that they’re not. And if your child has a confirmed food allergy, and you think he’s outgrown it, don’t start experimenting — get him reassessed by an allergist to make sure.

Angela Pirisi is a Hamilton, Ont.-based health writer and mom, who is happily plagued only by ragweed allergy.