There are several differences between autoimmune disorders and allergies. To understand these differences, it helps to know a bit about the immune system: Its job is to rid the body of foreign substances that might be harmful to it, such as bacteria and viruses, and also build protection against these invaders if they try to attack again. The process of getting rid of foreign substances and developing immunity is called "the immune response."
But sometimes the body's immune to a foreign substance doesn't function correctly, and "over-reacts" so fiercely that it produces symptoms. This is called an allergic reaction, and the foreign substance that triggers the allergic reaction is called an allergen. People can be allergic to many "foreign substances" -- shellfish, cats, plant pollen, to name but a few.
Other times, though, the immune response malfunctions and reacts incorrectly to the body's own normal tissues. It's as if the immune system "thinks" a part of the body is a foreign substance. It attacks the body, which is called an autoimmune response, and this happens in autoimmune disorders, such as multiple sclerosis, lupus and celiac disease.
In celiac disease, gluten stimulates (because of genetic predisposition) the production of immunoglobulins that attack the villi lining the small intestine (that is, the body's own normal tissues). Celiac disease is often confused for an allergic illness because (like an allergy) it requires a foreign substance to trigger it.
Another difference between autoimmune conditions and allergies is that autoimmune disorders are never outgrown; they persist for life. Allergies can sometimes be outgrown.
Also, autoimmune conditions can result in long-term damage to the body. For instance, because celiac disease damages the small intestine, people with celiac disease are at risk for malabsorption, nutritional deficiencies, iron-deficiency anemia, and osteoporosis. People with celiac disease are also at risk for other autoimmune conditions, such as thyroid disease, diabetes, and liver disease.
In addition, in untreated celiac disease, a type of white blood cell called the T lymphocyte is activated, along with other parts of the immune system, putting patients at increased risk to develop gastrointestinal lymphomas. A wheat allergy, in contrast, would not put patients at risk for any of these problems. In general, allergies usually result in only temporary symptoms without long-term damage, unless they produce a fatal anaphylactic reaction.