Chronic Headaches, Migraines, ADHD, Nasal Congestion, Runny Nose, Chronic, Frequent Colds, Chronic Idiopathic Urticaria, Cystic Acne, Diarrhea, Irritable Bowel, Bowelitis, Constipation, Distension Colic, Gastric in a large belly, easy to gain weight This could be a sign that you may be suffering from an allergy. But how do we know what causes an existing allergy? Therefore, allergy testing is important for us to determine the cause of the allergen at risk.