Coeliac disease is an autoimmune disease. It is caused by a reaction of the immune system to gluten – a protein found in wheat, rye and barley.
We know from research that those with the condition have genes which mean they may develop coeliac disease but we don’t yet know why.
When someone with coeliac disease eats gluten, their immune system reacts by damaging the lining of the small intestine. The small intestine is between the stomach and the large intestine (the colon).
In a healthy small intestine, there are small, finger like projections (villi) that allow the body to absorb nutrients from food into the blood. If you have coeliac disease, these villi become flat and you have difficulty absorbing nutrients.
In untreated coeliac disease, villi become inflamed and flattened together. In some cases, they can even disappear. This is called 'villous atrophy'.
When the gut is damaged in this way, it means the body can’t absorb all the nutrients from food properly. This is called 'malabsorption'.
The way the body's immune system reacts to gluten can affect other parts of the body as well. For example, the skin rash called dermatitis herpetiformis may develop.