Why some people get wheezy when peeling potatoesby Jennifer Bowden
As if living with hay fever isn’t enough, many people with oral allergy syndrome also react to certain foods.
ANSWER: Oral allergy syndrome (OAS) affects about three-quarters of hay-fever sufferers, says allergy specialist Dr Vincent St Aubyn Crump.
Crump, the author of Allergies: New Zealand’s Growing Epidemic, says the syndrome is prevalent in regions such as Queenstown and Gisborne. The symptoms of this secondary allergy are often mild, so many people are unaware they have it and habitually avoid foods that they react to.
Certain fruit, vegetables, nuts and seeds contain proteins with a similar structure to pollens. The immune system of hay-fever sufferers can confuse the two and start reacting to certain food proteins, says Crump, a consultant allergist at University Hospital of South Manchester. “It’s mainly due to a cross-reaction with birch pollen, but it’s also seen with grass and weed pollen cross-reactions.”
Unlike a primary allergy, such as that triggered by peanuts, which can lead to life-threatening anaphylaxis, OAS is usually localised. “The reason is that these allergens are labile and easily destroyed by the digestive enzymes in the gut.” So after causing symptoms such as swelling of the lips and/or itching or mild swelling inside the mouth or throat, the proteins are destroyed by the digestive system rather than being absorbed into the circulation as allergens.
Some people with the syndrome report nose and eye symptoms and itchy hands when handling raw potatoes or parsnips. So combined with the fact that it rarely causes anaphylaxis, or a severe reaction, “oral allergy syndrome” is a bit of a misnomer, Crump says. “Pollen food syndrome is a better term.”
Common triggers are raw fruit and vegetables, including apples, apricots, pears, cherries, kiwifruit, mango, plums, peaches, nectarines, tomatoes, carrots and celery. Other plant foods occasionally cause the condition, including raw peas, soy milk, and raw or stir-fried legumes such as bean sprouts.
Cooking can destroy the allergic effect of trigger foods. “Apples are one of the most common causes. However, people who get OAS from apples can eat them stewed without any symptoms.”
But in a small number of people, the syndrome causes a serious anaphylactic reaction. Typically, nuts are the trigger, says Crump. “The nuts commonly associated with pollen food syndrome are hazelnuts, almonds and walnuts. Again, it’s usually raw nuts that cause symptoms, whereas processed nuts, such as in chocolate spread Nutella, are tolerated.”
It’s important to distinguish primary nut allergies unrelated to pollen from OAS caused by nuts, he says. “If there is doubt, affected people should be assessed by an allergist, as occasionally an adrenaline auto-injector is needed.”
For those with OAS, the solution is cooking fresh produce to destroy the allergens. Offending fruit should be stewed. “Even a microwave will do it,” says Crump. Similarly, trigger vegetables should be cooked.
People who react to a wide range of foods may require expert guidance to manage the condition. Removing many fruits and vegetables from the diet could affect the intake of vitamin C and other important micronutrients.
This article was first published in the September 2, 2017 issue of the New Zealand Listener.
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