Basil allergies are rare, but the symptoms of this malady can be just as distressing as those of common food sensitivities. Reactions can cause hives, welts on the face and mouth, runny nose, itchy eyes, shortness of breath, nausea and vomiting shortly after consumption. The best remedy currently available is to avoid foods that contain basil, such as green curry sauce, pesto sauce and Italian seasoning. All Mediterranean and Italian cuisine should be eaten with care, as many dishes incorporate this spice.
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A basil allergy is the result of your immune system mistakenly identifying basil as a foreign invader. The first time you eat it, your body develops antibodies against it, as it would against a bacteria or virus. Molecules called immunoglobulin E, which your body designs to bond one or more basil compounds, attach to mast cells and await the next invasion. The next time you eat basil, the IgE-mast cell complexes bond to it, causing the mast cells to release chemicals that cause an allergic reaction.
One of the most notable chemicals the mast cell releases is histamine. This substance causes a phosphorous compound to bond to the cells that line your blood vessels, according to a paper published on the Davidson College website. This increases the distance between the cells and allows fluid to seep out into the surrounding tissues, causing swelling, hives, rashes and itching. Histamine can also cause your smooth muscles to contract, affecting your ability to breath, and mediate signals from your stomach to the emetic center in your brain, which triggers nausea and vomiting.
According to a study published in the "Annals of Allergy, Asthma and Immunology," plants that are in the same family as basil, such as oregano, thyme, mint, sage and lavender, may trigger a cross-sensitivity to basil. This means that if you are allergic to one of these foods, the IgE molecules that have been engineered to attack one spice may mistakenly attack basil as well. Medical scientists suspect that this is because all the plants in this family are molecularly similar, but they have not yet identified the exact allergen in basil.
Food allergies are not directly inherited, but you are more at risk if others in your family, particularly your mother, have these allergies, according to MayoClinic.com. The site also notes that people with asthma are more likely to have food allergies than people who don't. According to a study published in "Allergie et Immunologie," spice allergies appear to be exclusive to adults, especially adults who are allergic to mugwort and birch pollen.