Ask Dr. K: Food allergies may occur in those allergic to plant pollen

DEAR DOCTOR K: I’ve always had seasonal allergies. But over the past few years, I’ve noticed that my lips swell and my mouth gets irritated when I eat certain fruits and vegetables. Have I developed new food allergies as an adult?

DEAR READER: I suspect you’ve developed a type of adult-onset food allergy known as oral allergy syndrome. People with OAS suffer from hay fever and experience an itchy mouth, scratchy throat, or swelling of the lips, mouth, tongue and throat after eating certain raw fruits, vegetables or some tree nuts.

In people who have allergies of any kind, immune system cells that normally fend off germs become overactive. They respond inappropriately – setting off an allergic reaction – to otherwise harmless substances known as allergens. These allergens are often proteins, found in everything from pollen to pet dander.

Every protein has a distinct shape. The immune system is responding to these shapes. Some fruit and vegetable proteins have a similar shape to plant pollen – proteins that are shed by trees, grasses or other plants. People with OAS often already have allergies to plant pollen. When they eat fruit or vegetables that contain similar proteins, their overactive immune system goes to war.

If you have OAS, the food or foods that will trigger an oral allergic reaction depend on the type of pollen you’re allergic to:

• Birch tree: People with allergies to birch tree pollen often have OAS from peaches, apples, pears, kiwis, plums, coriander, fennel, parsley, celery, cherries, carrots, hazelnuts and almonds.

• Grasses: peaches, celery, tomatoes, oranges, cantaloupe, watermelon and honeydew.

• Ragweed: bananas, cucumbers, cantaloupe, watermelon, honeydew, zucchini, sunflower seeds, dandelion, chamomile and echinacea.

If a food you love causes a reaction, try cooking it. Peeling a fruit or vegetable before you eat it may also help. That’s because allergy-provoking proteins congregate near the surface. Finally, try taking an antihistamine about 30 to 60 minutes before eating a food that might give you OAS.