Some people sneeze like crazy. Others get itchy hives or watery eyes. But whatever the reaction, it boils down to one thing: allergies. If you have allergies, you have lots of company. As many as 30% of U.S. adults and 40% of children are in the same boat as you. While your problem may seem to start in the nose or the eyes, allergies actually come from an immune system run wild. Learning why these reactions happen can help you keep things under control and feel better.