Cross-reactions between similar allergens can be a potential source of danger for allergy sufferers. A well-known example is the birch pollen-nut-pome fruit syndrome. People sensitised to birch pollen have an allergic reaction to eating apples because the immune system mistakes the protein in the apple (Mal d1) for the structurally very similar protein in the pollen grain (Bet v1).Such a cross-reaction can cause various symptoms, such as:

  • Itching in the mouth and throat
  • Swelling of the mouth, tongue and lips
  • Hoarseness
  • Numbness
  • Swelling of the eyelids
  • Digestive problems

The same principle has been observed with different types of pollen. It is usually due to the systematic proximity of the plant species. Cross-reactions occur generally within the same plant family. Cross-reactions between families are rare and have mainly been observed in birch plants, sweet grasses, composite plants, olive plants, nettles and conifers.
Further information and a detailed list of cross-reactions, not limited to pollen, can be found in graphical form at the Allergen Avoidance Interest Group (IGAV).