A cross allergy or cross allergic reaction occurs if someone has become sensitized to a substance (primary allergy) and then reacts allergically to another substance with a similar allergen.
The cross allergy results from the allergen (the allergen-causing particle) in the second substance resembling the allergen in the first substance. One of the most common cross allergies is that between birch pollen and foods. As a consequence, there is a food allergy in addition to hay fever. The allergen in the birch pollen resembles many allergens in foods, so that a cross allergy can occur with, among other things, very many types of fruit. The name for this specific form of cross allergy is para-berry syndrome. In analogy, the combination of grass pollen allergy with food allergy is called the para-grass syndrome
English names for cross allergy are: cross-reactive allergy, pollen-associated allergy and in the case of food allergy pollen-related food allergy and pollen-food cross-reactive reactions. Known examples of cross allergy Milk, eggs, legumes and seafood
The allergens in the milk of different animal species, such as cow, goat, sheep and horse, show a great resemblance. An allergy to one type of milk also usually means an allergy to the other. Also in chicken and other birdlife is such a mutual connection.
In legumes this is not the case. Due to the differences, an allergy to one of the legumes such as beans, peas, soy, lentils, peanuts, licorice (pea family) or Johannesbrood does not automatically mean that there is also an allergy to one of the other species. Also with seafood like fish, squid, shrimps, crustaceans and the like, a cross allergy is less likely because the differences between species are high.
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