An Allergy is when the body is intolerant of certain things. A food allergy would see a person be allergic to nuts or dairy, and cause an upset stomach or perhaps even swelling of the throat. An environmental allergy would see a person be allergic to pollen or dust and cause them to sneeze or have itchy eyes. Another common symptom of an Environmental Allergy is Asthma, where the airways of the lungs become irritated and narrowed, making it very difficult to breathe.