Genetics plays an important role in the symptoms and severity of a person’s allergic reaction as does the amount of allergen the person has been exposed to. Reactions or symptoms of an allergy can range from mild to very severe to possibly life-threatening, and it all depends on the substance involved. Different allergic reactions manifest in different areas of the body and can affect sinuses, nasal passages, airways, lungs, mouth, lips and throat, skin, face, eyes, or the digestive system. These areas can experience itching, swelling, hives, wheezing or difficulty in breathing, cough or chest congestion, tingling in the mouth, or watery and itchy eyes. An urgent, life-threatening allergic reaction is called anaphylaxis.