For some people who have hay fever, fresh fruits, vegetables and certain nuts can trigger an allergic reaction that causes the lips/mouth to tingle or itch. It can also cause throat swelling or itching all over the body. This is also known as “oral allergy syndrome.” What causes this immune reaction? This reaction occurs because the structure of proteins found in some fruits and vegetables are identical to those found in pollen. These identical proteins confuse the immune system and ...