If taking a bite out of an apple makes the mouth tingle unpleasantly or eating celery leads to stomach cramps, a pollen allergy may be to blame. Doctors call it pollen-food allergy syndrome or cross-reactivity. An immune system that has been sensitized to allergy-causing proteins found in certain pollens can react to similar proteins in fruits and vegetables.
“Cross-reactions play a large role in adulthood,” remarked Joerg Kleine-Tebbe, an executive board member of the German Society for Allergology and Clinical Immunology. “We estimate that 5 to 10 per cent of the population is allergic to birch pollen alone.” The culprit is a stress protein in birches that protects them from viruses, bacteria and environmental stress. Other tree pollens and plant foods have similar proteins, which can confuse the human immune system.
“Consequently, 70 per cent of the people allergic to birch pollen have allergic reactions to apples, hazelnuts, cherries, peaches, carrots, celery and even soya beans,” Kleine-Tebbe said.
In many cases, only fresh fruits and vegetables trigger cross-reactivity. The cooking process and gastric acid in the stomach denature, or change the shape of, the allergens.
“Physical reactions to consumption of the foods are mostly local in nature, such as redness, swelling or itching of the mucous membrane in the mouth and throat, also called oral allergy syndrome,” noted Thomas Werfel, a physician at Hanover Medical School’s Clinic for Dermatology, Allergology and Venereology. Unlike classic food allergies, pollen-food allergy syndrome produces reactions like asthma attacks relatively rarely.
“Isolated cases can, however, be very dangerous, for example when the throat swells completely shut,” Kleine-Tebbe said.
A pollen-related food allergy can arise in any period of life — whenever the body has been sensitized to the main trigger. “Many patients develop hay fever in reaction to birch pollen and, at the same time, a food allergy,” Werfel said.
“When someone has hay fever, a pollen diagnosis is usually made; it’s easy to neglect the foods,” noted Sabine Schnadt, spokeswoman for the German Allergy and Asthma Association. But avoiding all suspicious foods makes little sense, she said, “Too many foods would then be avoided, which could lead to a deficiency of certain nutrients.” Step two is proof of sensitivity. Adults are often given a skin prick test, Kleine-Tebbe said. An alternative is a blood test, which measures the amount of allergy-causing antibodies in the bloodstream, known as immunoglobulin E (IgE) antibodies. If the test results are inconsistent with the person’s medical history, provocation (challenge) food testing at a special centre is done, in which a person is exposed to a suspected allergen under controlled circumstances.
A multi-pronged approach is used in therapy. The patient is told to avoid the allergy-inducing food altogether or, if it is only a problem when eaten fresh, to cook it before consumption. Nuts and celery are used as ingredients in many foods, however, which makes it harder to avoid them.
“Nutrition counselling is quite helpful in making dietary adjustments,” Schnadt said. But when allergy symptoms are strong, the use of medications is often necessary.
