Many people have discovered their food allergies by tracking the reactions they have to different foods in a personal health journal. Your rash could be a symptom of food allergies. Other symptoms include swelling or itching in the mouth, itching, hives and eczema, wheezing and nasal congestion or trouble breathing, swelling of the tongue, throat, lips or other body parts, abdominal pain ot flatulence, diarrhea, vomiting or nausea, fainting, lightheadedness...