Family health

Food allergy facts

Read on to find out how allergic reactions are triggered

By Wendy Haaf
Food allergy facts

Maria Pavlova/iStock

Just a taste won’t hurt.” Despite her own allergic background, Grandma didn’t understand why her daughter was making a big deal over the dollop of ice cream poised a few centimetres from the lips of the younger woman’s six-month-old.

Sure, hay fever ran in the family, but no one in the clan was allergic to milk, so why should the little one wait until her first birthday for that first scoop of vanilla ice cream?

Tendency Inherited
While severe, life-threatening food allergies affect only one or two people in 100, approximately eight percent of children, age two to three years are allergic to one or more foods, and the odds of developing such sensitivities increase if a child has a family history of what doctors dub atopic disease — food allergies, hay fever, eczema or asthma.

If you have one of these conditions, “your kid’s more likely to be allergic in general, but what he’s allergic to, whether food or pollen, isn’t predictable,” explains D. William Moote, an allergist at London Health Sciences Centre in London, Ont. Children with one allergic parent run about a 30 percent chance of developing some sort of allergy, including food allergies. Two allergic parents doubles those numbers.

But why does a family tree featuring non-food allergies up the odds a child will react adversely to something she eats? And how does delaying the introduction of certain foods help?
Immune Error
Allergic reactions are triggered by infection-fighting cells that mistake an otherwise harmless substance for an invader, and experts believe this hyperalert immune system is passed from one generation to the next. Allergic people produce greater-than-normal amounts of IgE, the body’s burglar alarm, which detects intruders and instructs special blood cells to fire the chemical barrage that triggers allergy symptoms. In a child with hay fever, ragweed pollen may trip the switch, while peanut protein pushes the button in children with an allergy to that food.

What prompts a child’s body to decide peanuts, milk or egg is the enemy? Think of the intestinal lining as a net, with tiny holes, that allows food molecules to slip through only after they’ve been broken into very small pieces. Before six months of age, a baby’s digestive system is less developed and unable to break down food as easily as adults. That means if foods are introduced early, bigger, more recognizable chunks can float into the bloodstream. The immune system may then inadvertently label a food protein as an offender, prompting it to attack when it next encounters that substance.

Is Prevention Possible?
Many experts believe delaying the introduction of certain foods until a baby’s immune system is more mature may stop this cycle before it begins, thus fending off some food allergies. Consequently, most physicians recommend exclusive breastfeeding for four to six months and switching to formula if you wean before a year. (If your family is highly allergic, your doctor may suggest a “predigested” formula: These products are thought to reduce the risk of setting the allergy cycle in motion because the milk proteins they contain are broken into tiny, less recognizable, bits.)

Even if neither you nor your partner have a history of allergy, most health professionals now advise waiting to introduce the foods most apt to cause allergies:
• milk and soy (12 months);
• eggs (12 to 18 months);
• shellfish, peanuts, nuts and seeds — including peanut butter; and sesame paste (3 years).

If allergies do run in your family, consult your doctor for individual recommendations.

So far, scientific studies haven’t definitively determined whether this strategy does, in fact, prevent allergies. “These recommendations are mainly based on observations that most of these food allergies occur in children under age three,” acknowledges Zave Chad, a paediatric allergist in Ottawa.
Is My Child Allergic?
So when should you suspect your child may have a food allergy? Signs and symptoms are relatively easy to pick up, if you know what to watch for.

A good clue is a rash or hives appearing within minutes to a few hours of eating a particular food, says Moote. St. Marys, Ont., mom Monika Gibson remembers her son, Kyle, blossoming with hives after he spit out a peanut-butter-smeared cracker he hadn’t even chewed. (Mild rashes around the mouth don’t necessarily signal allergy, notes Moote, since this can occur when acidic foods such as tomato sauce irritate the skin.) Flare-ups of eczema — an allergy-linked condition where skin periodically breaks out in dry, itchy, red, scaly patches — may also hint at food allergy.

Swollen lips, tongue or throat, cough, wheezing and shortness of breath can also herald an allergic reaction. If your child experiences any of these problems, take her to the emergency department immediately.

Sometimes, the digestive system is affected: projectile vomiting (usually immediately after eating an offending food), diarrhea, blood or mucous in the stool and even failure to thrive (not growing or gaining weight as well as expected) can all indicate food allergy.

Diagnosis and Treatment
If such symptoms lead you to suspect your child has food allergy, you should investigate, advises Monika Gibson, who is the Ontario coordinator for the Allergy/Asthma Information Association. Your family physician or paediatrician can refer you to a specialist (an allergist or gastroenterologist, depending on your child’s symptoms) who will help determine what kind of detective work is required to single out the culprit. Together with detailed questions (a calendar can help you keep track of your child’s attacks and the foods he eats each day) a skin test (applying a minute amount of food extract to a skin prick to see if it provokes a reaction) or special blood test may help narrow the list of suspects.

In kids with digestive problems, diagnosis may be trickier. “Sometimes it’s hard to get a clear diagnosis,” says Valerie Marchand, a paediatric gastroenterologist at St. Justine’s Hospital in Montreal. “Most of the time, the best diagnostic tool is to remove the suspected offending food from the diet, and see whether symptoms improve,” she explains. (This usually involves avoiding any trace of the food, and others that are closely related, for at least a week or two.)

Once a food allergy is diagnosed, the main treatment is cutting the food out of the child’s diet entirely. A breastfeeding mother should eliminate that food from her diet since the protein can be secreted in breastmilk, says Chad. (Many doctors believe continued exposure to even small amounts of the allergen may reduce a child’s chances of outgrowing a food allergy by keeping the immune system in a state of alert.)

If your baby is still under a year old and she’s allergic to cow’s milk, this may be a simple matter of switching to a predigested formula and avoiding dairy products.

Otherwise, eliminating a food may be a bit more difficult. A registered dietitian can help you learn to read food labels, since some foods are referred to by many different names, and help you ensure your child gets the nutrients he needs. (You may also want to carefully check labels of products like kids’ skin care products, since a recent US study found more than one-quarter of such items researchers tested contained common food allergens.)

If your child has a food allergy that’s been confirmed with a skin or blood test, your doctor will also recommend that you prepare for the possibility of anaphylaxis — a dangerous, potentially life-threatening reaction involving more than one body system (say, hives plus asthma, or breathing problems and a swollen throat). While anaphylaxis is relatively uncommon, when it does occur, minutes count.

“You have to have treatment available just in case you get a severe reaction,” says Moote, because there’s no way to predict the severity of the next allergic attack. Adrenalin (administered with an easy-to-use injector pen) quickly counteracts swelling until your child gets safely to hospital. Your doctor may also advise you to carry an antihistamine to help ease allergy symptoms.

Happily, however, most children with food allergies never have to use the adrenalin kit, and many of them outgrow their allergies over time. “About 80 percent of kids outgrow milk and egg allergies, and 20 percent will actually outgrow a nut allergy,” reassures Chad. And with a little extra care, even those who don’t shed their allergies will grow up happy and healthy, like now-13-year-old Kyle Gibson.
Allergy or Intolerance?
What’s the difference between a food allergy and a food intolerance? While some symptoms of the two conditions (nausea, vomiting, diarrhea and failure to gain weight) overlap, allergies stem from an overzealous immune system, while food intolerance involves an inability to digest certain substances. One of the most common examples of the latter is lactose intolerance, often linked to too-low levels of lactase, the enzyme that breaks down one of the main sugars in milk. Gas, bloating and cramps that come on within two hours of eating dairy products can also signal lactose intolerance.

Food Allergy Fictions

Each allergic reaction will be a little worse than the last one.
False, says Dr. Moote: There’s no way to predict whether the next reaction will be milder or more severe than the last.

My child ate a bite of a peanut butter cookie without having a reaction — she must have outgrown her allergy, so it’s now safe for her to eat peanuts.
About 40 percent of the time, people who are positively allergic to a food don’t react at all when they’re exposed. Before you resume feeding your child something she’s allergic to, your allergist will need to conduct a “challenge”— giving small amounts of the food in a medically supervised setting.

If you wipe peanut butter on a child’s cheek and the skin doesn’t turn red, it’s safe to feed it to him.
Not only can this practice not detect allergies reliably, it could be downright dangerous if a child does in fact turn out to be allergic.

A baby can have an allergic reaction the first time she eats a particular food.
Actually, it usually takes several exposures before the immune system starts mounting attacks on a particular food protein.

Pregnant and nursing mothers should avoid eating highly allergenic foods because they can pass into breastmilk, triggering sensitivities in certain children.
Actually, there’s still some debate on this point. Allergists Chad and Moote don’t recommend a pregnant or nursing mother avoid any foods to which she herself is not allergic, arguing that keeping a mother on a strict diet may interfere with her baby’s growth. On the other hand, if both parents come from highly allergic families, or already have one child with a food allergy, Marchand suggests mothers eliminate the most common food allergens from their diets during the final weeks of pregnancy and during breastfeeding. This is an issue to talk over with your doctor.

Allergy/Asthma Information Association, 1-800-611-7011,
Food Allergy & Anaphylaxis Network,
Canadian Allergy, Asthma and Immunology Foundation,
The Complete Allergy Book, by June Engel. Key Porter 1997, $19.95
The Complete Kid’s Allergy & Asthma Guide, by Milton Gold (ed.), Robert Rose 2003, $34.95

This article was originally published on Oct 22, 2004

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