Hello. Food allergy can be due to anything. Personally the most practical way to identify the food causing allergy is to keep a food diary. I would suggest you to keep a note of each and every food your daughter consumes with time and date and also note the time and date of symptoms. Please note ingredients of each food items too. Your keen observation will help you to identify the food causing allergic symptoms. I would like to let you know that most common foods causing allergy are - milk, peanut, treenuts, soy, eggs, shellfish, fish & meat. However, it is possible to have allergy for any of the foods, so food diary is indeed a handy tool. Rast tests are used for diagnosis of food allergy but they are not 100%. It is possible to have a negative Rast test despite having allergy to food and also vice versa. Also, sometimes a child can have non-allergic reaction to a food, which cannot be picked up in laboratory tests. If this approach does not lead you to any conclusion, I would suggest you to consult an allergist-immunologist, who will ask you in very much detail and may suggest you some investigations. He may also advice you to keep a food diary. Hope this will help you. Wish your daughter the best of the health. Regards.