When someone says he has an allergy to gluten, he usually means he has a gluten intolerance.
When a person has a food allergy, his immune system has determined that that food is dangerous to the body and he has a reaction to the food. The immune response symptoms (such as hives, itching, swelling, trouble breathing, abdominal pain, diarrhea, dizziness, nausea, vomiting) are time-limited and in most cases they don't cause lasting harm to the body. The exception to this is when a food allergen causes an anaphylactic reaction, which is life threatening. If you have a food allergy, it may be temporary. Children often grow out of food allergies by age five.
Gluten intolerance is a food-induced reaction that is unrelated to the immune system. It is a reaction of the digestive tract that causes gastrointestinal symptoms when the sufferer eats foods containing gluten, a protein found in wheat and other grains. Unlike allergies, intolerances cannot be measured by antibody tests, which measure immune responses. The only way to diagnose a gluten intolerance is through an elimination diet. Eliminate any foods you suspect might be causing the symptoms. When the symptoms stop, you can begin slowly reintroducing the foods one at a time. This is called an "open challenge." When the symptoms reappear, you will know which food was the culprit.
There is no treatment or cure for gluten intolerance. You will have to follow a gluten-free diet if you don't want to deal with the symptoms. You may find, however, that rather than being gluten intolerant, you just have a gluten sensitivity. In this case you may be able to tolerate a low-gluten diet instead of eliminating gluten from your diet altogether. You should consult your physician or a dietician to help you determine what diet is right for you.