Allergic reactions to parsley are most likely to be caused by Bet v 1-like proteins, which cause reactions in people sensitised to birch tree pollen and give oral allergy type symptoms.
Lipid Transfer Proteins (LTP) have been identified in parsley, these proteins are resistant to heat and are found in many types of plants. Patients suffering from a more severe allergy to cooked fruit may be sensitised to this group of proteins
Another suggestion is that plants in the Apiaceae family contain profilin proteins which can cause allergic reactions in uncommon circumstances.
Parsley contains terpens, which can cause contact dermatitis and eye and nasal itchiness.
Allergy to parsley is loosely linked to Pollen Food Allergy Syndrome. You may have Pollen-Food Allergy Syndrome if you suffer from dill allergy with oral allergy symptoms to 3 or more of the foods mentioned in the cross reactivity section.
You may be suffering from LTP Syndrome if you have reactions to various fruits, vegetables and nuts and your reactions continue to be severe after you have discarded the peel and have cooked the food.
Parsley is in the family Apiaceae, other spices in this family are coriander, caraway seed, celery, chervil, cumin, dill, fennel and aniseed.
If sensitised to Birch pollen you may have Pollen Food Allergy Syndrome and may also react to Apple, Carrot, Kiwi, Pear, Peach, Plum, Nectarine, Apricots, Cherries, Tomato, Celery, Potato, Parsnip, Pepper, Cumin, Peas, Dill, Fennel, Hazelnut, Walnut, Almonds, Coriander, Peanuts, Lentils and Beans.
Common foods involved in LTP allergy include hazelnuts, almonds, walnuts, apples, dried fruit, lettuce and tomatoes.