Patients who have allergy to ragweed pollen can experience itching of the lips , mouth and throat when they eat fruits such as melons. Sometimes, itchy bumps can develop in the mouth within minutes after eating such fruits.
This condition is described as oral allergy syndrome. In this condition, when a person develops allergy to ragweed pollen, allergy antibodies (IgE) to ragweed is made by the immune system. When these antibodies react to ragweed pollen in the nose, allergic rhinitis results. Sometimes, these same antibodies will react to fruit containing similar allergens found in both the fruit and the ragweed pollen. So when a person eats such fruit, the same allergic reaction that occurs in the nose is occuring in the mouth. Depending on the individual, symptoms can range from mild (itching) to severe (throat swelling)
Fortunately, this condition is usually mild and self limiting. Symptoms can usually be relieved by antihistamines. Cooking the fruit will also remove allergic reactions because the cooking process changes the structure of the allergens in the fruit.
However, patients should not just take antihistamines to reduce their symptoms of oral allergy syndrome in order to eat more of such fruits. There is concern that by suppressing these symptoms and eating more of the fruit, a more severe allergic reaction might occur later on. Talk to your Allergist, appropriate immunotherapy (by a board certified Allergist) has been shown to reduce the symptoms of allergic rhinitis and oral allergy syndrome.