For people who aren’t allergic, kiwi is one of those perfect foods: each one packs in as much potassium as a banana, more than the recommended daily dose of vitamin C – even more than an orange – as well as high levels of beta-carotene. It’s also rich in vitamin A and E, and its seeds are rich in alpha-linoleic acid, an omega-3 essential fatty acid. They’re high in fibre and have antioxidant properties, so are considered great cancer fighters.

How kiwi fruit allergies work

For all its benefits, however, the fruit can be extremely problematic for those who develop allergies to it. Most reactions are limited to itching and inflammation in the mouth and throat (this is usually linked with oral allergy syndrome), but others can experience more serious symptoms, including abdominal pain, vomiting, difficulty breathing, and in very rare cases, anaphylactic shock and death.

Part of the reason why kiwi has become such a prevalent allergen is that it cross-reacts with many other foods and substances, including birch pollen, avocado, banana, rye grain and hazelnuts, meaning the allergens share similar properties and can react the same way in the body.

It can also spell trouble for people with sensitivities to latex – which is common among health care workers – because while the substances seem fundamentally different, they share common epitopes, so the immune system sees them as the same thing.

How common are kiwi allergies?

Amazingly, kiwi first arrived on North American shores just 50 years ago, in 1962, and kiwi allergy was first reported fairly recently, in 1981. But since that time, kiwi allergies have become one of the most common allergies in Europe, with one study finding that four percent of allergic kids tested positive, and another showing that nearly half of food allergic patients in Sweden and Denmark reported reactions to the fruit.

Some researchers suspect that there is a geographic component at play, and that where there is more birch, there’s likely to be more kiwi allergy. The numbers have also shown a steady increase in North America.

But while people with latex and birch pollen allergies are at elevated risk for kiwi allergy, they shouldn’t eliminate the fruit from their diets unless they experience an adverse reaction – and if they do, they should talk it over with their allergist.

Related:

• Oral allergy syndrome: When raw fruit is forbidden
• Why do pollens and foods cross-react?
• How John Grisham solved his allergy mystery

Dr. Waserman: Oral allergy syndrome is seen in birch tree or ragweed pollen allergic individuals  who may develop symptoms on ingestion of certain raw fruits, vegetables, or tree nuts.

Symptoms typically consist of itching, tingling or  swelling of the mouth, lips, and throat. An allergic reaction happens when the foods are eaten raw. Once the foods are cooked, they can be eaten safely.

Jams are prepared by heating the particular fruit. If you experienced symptoms after peach jam, you may have a true food allergy to peach, and not just an oral allergy syndrome. I highly recommend consultation with an allergist for assessment and skin testing to help sort this out.

We welcome your question to Allergic Living’s Ask the Allergist. Thank you for understanding that the specialists aren’t able to answer every question received.

Dr. Susan Waserman is an allergist and Professor of Medicine in the Division of Allergy and Clinical Immunology at McMaster University in Hamilton, Ont. She is also a past president of the Canadian Society of Allergy and Clinical Immunology.

But the patients coming through Ham Pong’s offices in Ottawa and Vancouver were telling a very different story. Not only were more of them reacting to sesame, but those reactions tended to be severe; in fact, more of his patients were experiencing full-blown anaphylaxis from eating sesame products than from shellfish.

A more formal survey of more than 2,000 patients confirmed the allergist’s suspicions – but many of his colleagues were still not convinced. “I presented a study at an allergy meeting, and one of the allergists didn’t believe that sesame was a problem. So he asked parents for a show of hands of how many of their children had sesame allergy, and he was very surprised “at how many hands went up,” recounts Ham Pong. “It took him aback because there was no published literature on its prevalence at the time.”

Since then, there has been a significant amount of scientific literature to show that sesame is yet another one of those especially problematic foods, to the point where the European Union and Canada have added it to their priority allergen lists, which include peanuts, tree nuts, dairy, wheat, eggs, fish, shellfish and soy. The United States is investigating whether to follow suit.

But sesame isn’t the only new culprit to gain priority status in Canada; nor is it the only emerging allergen on the radar of North American scientists. The fact is, our diets are constantly in flux – often because particular foods are found to have special disease-fighting properties and become trendy, or because people from around the world bring their culinary influences with them when they arrive on North American shores.

In turn, those foods – from sushi to hummus to curry – get woven into our ever more colorful mainstream diet. Those constantly changing grocery lists, however, mean that our society’s allergies are bound to see shift as well.

“Until kiwi became popular because of the high levels of vitamin C, you didn’t see a lot of kiwi allergy – but now you see a fair amount because it’s a very allergenic fruit,” says Ham Pong. “But if there wasn’t much of it in the diet, it wouldn’t really be an issue. So what makes a food a problem in society is how allergenic the food is, and how much that food is adopted as part of the daily diet.”

Open Sesame

That’s likely what happened with sesame, says Dr. Robert Wood, director of pediatric allergy and immunology at the Johns Hopkins University School of Medicine in Baltimore. The seed became more common in breads, the popularity of traditional Middle Eastern foods such as hummus skyrocketed, and bagels, which are often coated with sesame seeds, became a mainstay in the mainstream North American diet.

And unlike some oils such as peanut and corn whose proteins are almost entirely removed during the refining process, Wood adds that sesame is a raw oil, and as a result can be just as allergenic as the seeds themselves.

“In our practice, it has become much more common, and appears to be the fourth or fifth most common allergen we deal with,” says Wood. In addition to pointing the finger at the increased prevalence of sesame in our diets, Wood says that one of the most notorious allergens on the list may also be adding to the problem.

“We see sesame allergy more commonly in children who also have a peanut allergy, and we suspect that there are some similarities in the allergens in sesame and peanuts,” he explains. “So there may be some of the sesame allergy that’s actually being driven by the increase in peanut allergy.”

But because the prevalence of sesame allergy is relatively new, regulatory bodies have yet to catch up. In the United States, food manufacturers must clearly declare the top allergens on its product labels – but as yet, sesame has not yet made that list, so it can still be hidden as “tahini”, “spices” or “natural flavouring”. (It’s also used in cosmetics and pharmaceuticals.)

In Canada, sesame was added to the priority allergens list in 2000, and mustard is in the process of being added as well, but the country has yet to enact new regulations that require manufacturers to label all priority allergens in clear language.

Peanuts are the most common legume that people will react to, and about 5 per cent of peanut allergic people will react to other legumes, such as beans, peas chickpeas and lentil.

In general, food allergy is on the rise in North America and other developed countries. In Canada, an estimated 7.5 per cent of people have food allergies, representing more than 2.5 million people. In the United States it’s estimated that 12 million Americans (or just under 4 per cent of the population) have food allergies.

A major study in the United States recently found that cases of peanut allergy in children more than tripled in a decade, and that more than 3 million Americans now have a peanut or nut allergy.

Here are the rates of some of the major allergens in Canada and the U.S.

CANADA

Source: Surveying Canadians to Assess the Prevalence of Common Food Allergies and Attitudes towards Food LAbelling and Risk (SCAAALAR) study. Published in the Journal of Allergy and Clinical Immunology, June 2010.

UNITED STATES

Peanut, Tree Nut or both:
Children -  2.1 %
Adults – 1.3 %

Source: US prevalence of self-reported peanut, tree nut, and sesame allergy: 11-year follow-up. Published in the Journal of Allergy and Clinical Immunology, June 2010.

Milk and egg allergy are both common in children. In the United States, 2.5 per cent of children under the age of 3 have a milk allergy. Egg allergy affects 1.5 to 3.2 per cent of children.

The good news is many children outgrow their allergies to milk and egg.

Source: AAAAI

A less severe form of food allergy, called oral allergy syndrome, is a reaction to proteins in common raw fruits, vegetables, nuts and seeds. It’s called “oral allergy” syndrome or OAS because its symptoms are usually limited to the lips, mouth, tongue and throat.

Estimated to affect about one-third of pollen allergy sufferers*, oral allergy sydrome (sometimes called pollen allergy syndrome) is more widespread than the higher profile – and more dangerous – allergies to peanuts, dairy and eggs.

If you have oral allergy syndrome, chances are that you also have allergies to pollen from trees such as birch and alder, and/or to pollens from ragweed and grass.

Think of it as an allergy by association – or a cross-reaction – because your immune system, already primed to attack tree, plant and grass pollens, does not recognize the subtle differences between their proteins and those contained in foods as basic as an apple.

Not Usually Life-Threatening

One reason for oral allergy syndrome’s lower profile is that, unlike other food allergies, its symptoms are not usually life-threatening. Another is that it is relatively easy to avoid.

“You may eat something that contains traces of peanut, dairy or egg, but you aren’t going to unknowingly bite into a raw apple,” notes Dr. Antony Ham Pong, an allergist and based in Ottawa.

High Incidence of Oral Allergy Syndrome

About 10 per cent of the population**, or roughly one-third of North Americans with pollen-related allergies, are thought to be affected by OAS.

Ham Pong says he usually first sees patients when they’re between 8 to 10 years old. It’s not clear, however, why no more than one-third of hay fever sufferers are affected.

Next: More Serious Oral Allergy Symptoms

AS FRIENDS herald spring’s arrival with the glee of a lottery winner, it’s often hard for the allergic to join the celebrating. They know that their tree foes – birch, elm, maple, alder, poplar and their nasty ilk – have begun to churn out clouds of tiny allergy-causing pollen.

Not only do a third of us battle hay fever – with runny noses, sinus and eye symptoms – but for a significant proportion of allergy sufferers, the spring bloom is just the start of their allergy woes. Dr. Antony Ham Pong, an Ottawa allergist and clinical researcher, estimates that up to 10 per cent of the general population has a condition called oral allergy syndrome, or OAS.

It’s a less severe form of food allergy, directly related to pollen reactions, that’s known to set off tingling and unpleasant itching in the mouth, throat and lips. Reactions are caused by a variety of fruits, vegetables, nuts, seeds, and even spices; all of which share allergenic proteins with specific hay fever-causing trees and plants.

“Nobody talks about the foods causing oral allergy syndrome because it’s not considered a life-threatening allergy,” says Ham Pong, the author of several articles educating patients and doctors about oral allergy syndrome. “But it’s actually more common than peanut, milk, egg, and fish allergy.”

In springtime, two of the biggest cross-reaction offenders are birch and alder trees. Depending on where you live, anywhere from 20 to 70 per cent of people who are allergic to birch and alder pollens will also have oral allergy syndrome.

Ham Pong estimates about a third of birch-allergic North Americans are affected, but the incidence of oral allergy syndrome is even higher in some European countries. Although OAS is relatively common, he doesn’t think it is increasing, at least not in North America. Rather, doctors have become better at spotting this condition.

But how can a tall, skinny tree that gives you the sniffles cause an itchy mouth if you chew on a celery stick?

Next: How the immune system gets confused

A life with OAS means only cooked or baked fruit. Crisp, raw fruit, how I miss you.

Cradling a fresh, succulent peach in my hands, I take in its tantalizing aroma. I rub the fuzz lightly on my lips before taking a big, juice-dripping bite. Delicious.

I swallow, and the tingling begins. First on my tongue, then throughout my mouth and my throat. Tingling becomes itching: there is no stranger feeling than an itchy tongue. That bane of the fruit-loving, Oral Allergy Syndrome, has kicked in.

OAS (also known as pollen-food syndrome) is an allergic reaction to certain proteins in a variety of fruits, vegetables and nuts. The symptoms include itching and burning of the lips, mouth and throat. In more serious reactions, there may be swelling of the mouth, back of the throat and windpipe as well as hives.

Those of us with the condition usually develop symptoms within minutes of eating the food, and they typically dissipate in less than 15 minutes. Just enough time to make a person go a bit crazy.

For me, the itching can be counteracted by eating a neutral substance such as bread or by drinking water. Fortunately, OAS is rarely severe.

“For the majority of people, this is not a real life-threatening problem like true food allergies,” explains Dr. Bruce Mazer, director of the division of allergy and immunology at Montreal Children’s Hospital and an associate professor at McGill University.

Raw vs. Cooked
OAS sufferers react to raw fruit, but are usually able to eat the same food cooked without a problem. “Typically we see OAS in people allergic to heat labile protein, which means those proteins easily destroyed by heat,” explains Dr. Paul Keith, an associate professor of allergy and clinical immunology at McMaster University in Hamilton.

“When you eat the fruit raw, it’s your own body’s heat that breaks down the protein, which is why the reaction doesn’t move beyond the mouth, says Keith, who’s also an investigator for AllerGen, the allergy research network.

I know the raw versus cooked issue first-hand. When I eat uncooked fruits like apples, cherries, pears and my beloved peaches, they all cause itching. But bake them in a pie and I can eat to my heart’s content, without so much as a tingle.

I remember eating apples as a youngster with no problems, but then one day, my tongue got really itchy afterward. As my mother couldn’t see anything on my tongue, she assumed I was trying to get out of eating the fruit. Then it happened again, and with different fruits. Because they couldn’t see a problem, my parents thought I was just fussing. But they did stop giving me the troublesome fruits.

By my late teens, I started trying these fruits again, in small amounts. Sometimes I got an intense itch in my mouth and throat, sometimes it was minor. If I craved the juicy goodness, I’d eat the fruits anyhow – since the itch always went away.

Once, however, I ravenously ate a whole peach. This time itchiness turned to swelling: my lips got puffy and I felt like I couldn’t swallow. The episode subsided in half an hour. I was miserable, yet vindicated, since my parents finally believed there was an allergic reaction. We asked a couple of doctors, but no one could pinpoint the condition. They advised that I avoid the offending fruits like any major food allergy, and that put an end to my fruit infatuation.

Fortunately, awareness of OAS is growing. But how can you be sure if you have it?

Next Page: Diagnosing OAS