When it comes to allergies and allergic reactions, the symptoms can range from a simple rash to a more severe form of reaction termed anaphylaxis, which often causes the swelling of various body parts including that of the tongue and can lead to a complete shutdown of the body. If you are not sure whether you are allergic to say, peaches, or for that matter any substance then you can always visit your physician to get a simple test done which should enable your doctor to assess your sensitivity to the substance in question. You can also request your physician to run a complete allergy panel test which should highlight all the allergens that you are susceptible to, so that you can take better care of your health.