You do not necessarily have to avoid any foods if you have ragweed allergies; however, you may find that your allergy symptoms worsen when you eat some foods. If this is the case, you should discuss it with your allergist, and you may have to avoid those particular foods, at least during ragweed season.
Ragweed is a weed whose pollen causes seasonal allergies (also known as hay fever or allergic rhinitis) in millions of people. Although the usual symptoms of ragweed allergies are sneezing, runny or stuffy nose and itchy, watery eyes, it is also known to cause oral allergy syndrome (OAS or pollenfood syndrome). This causes the worsening of allergy symptoms after the consumption of fresh vegetables and fruits. Other symptoms of oral allergy syndrome include mild swelling (angiodema) and itchiness of the throat and mouth.
The cause of oral allergy syndrome is a cross reactivity between the proteins in airborne ragweed pollen and the proteins in vegetables and fruits. Sometimes the immune system in someone who is allergic to pollen recognizes a similarity between the pollen's proteins the proteins of the food. The immune system reacts by trying to fight off what it thinks is dangerous to the body. This reaction is what causes your symptoms.
The foods that most commonly cause oral allergy syndrome in ragweed allergy sufferers are banana, chamomile tea, cucumber, dandelion, Echinacea, melon (cantaloupe, honeydew and watermelon), sunflower seeds and zucchini. If your seasonal allergy symptoms worsen after you eat these foods (in a raw state) and you experience symptoms limited to your mouth and throat, you may have oral allergy syndrome. You should see an allergist for a proper diagnosis and to discuss the best way to manage your symptoms.