People with gluten intolerance (celiac disease) are extremely sensitive to the protein gluten, which is found in wheat, barley, rye and possibly oats. The condition involves an inappropriate immune system reaction to gluten that causes inflammation in the small intestine.

This inflammation damages the interior wall of the small intestine, specifically harming tiny protrusions called villi. These villi are responsible for absorbing nutrients into the bloodstream. The loss of the villi often leads to malnutrition and related complications such as bone disease.

Although patients with other food intolerances may tolerate "small amounts" of the problem food without triggering a reaction, people with gluten intolerance cannot safely consume any amount of gluten. Though some people may believe they can tolerate a small amount of gluten because symptoms do not occur, ingestion can still result in damage to the small intestine.

Though symptoms may appear similar, gluten intolerance is not a food allergy because the immune response to gluten is different than an allergic reaction. The immune system turns upon itself with both conditions, but gluten intolerance results in specific damage to the small intestine. A food allergy, though, often results in a more generalized reaction that occurs as histamines travel throughout the bloodstream. Although it is possible to have a food allergy to wheat and wheat protein, this condition is not related to gluten intolerance.

About 2 million Americans suffer from celiac disease, according to the National Institutes of Health. It is not known what causes gluten intolerance, though genetics has a role. A person is more likely to have gluten intolerance if an immediate family member also has the condition. For some reason, also unknown, the condition is sometimes triggered by a trauma such as injury, pregnancy or severe stress.

Gluten intolerance can lead to a variety of complications if not treated by a physician. The most frequent complications involve malabsorption (the inability of food to properly digest and move through the wall of the intestines into the bloodstream) and malnutrition (a lack of sufficient vitamins or minerals that results from the poor absorption). This lack of proper nutrition leads to many of the symptoms and complications associated with gluten intolerance. Because levels of malabsorption vary in each case, symptoms also vary in type and intensity. Some people with gluten intolerance suffer severe symptoms, but others suffer from none at all.

In addition to the dangers of malnutrition and malabsorption, gluten intolerance can increase a person's risk of developing a number of serious conditions. These include type 1 diabetes, lupus, rheumatoid arthritis, other autoimmune diseases and certain forms of cancer.