 [ Symptoms ] when i eat nuts i break out in cold sores canker sores and neck rash is this a common reaction [ Disease ] there are many potential mechanisms by which food may cause symptoms allergic reactions are caused by allergic antibodies leading to immediate hypersensitivity reactions nut allergy typically causes itching liptongue swelling nausea vomiting lightheadedness flushing andor rash the rash is usually hives welts but some develop other types of skin eruptions ulcers in the mouth is an unusual manifestation make a list of all the foods that cause the symptoms timecourse of development of symptoms in relationship to eating the food so your doctorallergic can further investigate