Allergies occur when the immune system overreacts to harmless substances (allergens). Allergies can significantly affect quality of life. They are among the most common chronic childhood diseases. Common Symptoms: Respiratory - Sneezing, coughing, runny/stuffy nose, wheezing, chest tightness, throat closing. Skin - Itching, redness, hives, swelling (including lips, mouth, or throat). Eyes - Redness, tearing, itching. Digestive - Nausea, vomiting, diarrhea, abdominal cramps. S