Coeliac disease is caused by an abnormal reaction by your immune system to the protein gluten, found in foods such as bread, pasta, cereals and biscuits.

Some people with coeliac disease find eating oats can also trigger symptoms.

Coeliac disease is an example of an autoimmune condition, when your immune system mistakes healthy cells and substances for harmful ones and produces antibodies against them (antibodies usually fight off bacteria and viruses).

In the case of coeliac disease, your immune system mistakes one of the substances that makes up gluten, called gliadin, as a threat to the body.

The antibodies cause the surface of your intestine to become inflamed (red and swollen).

The surface of the intestine is usually covered with millions of tiny tube-shaped growths called villi. Villi increase the surface area of your gut and help it to digest food more effectively.

However, in coeliac disease, the damage and inflammation to the lining of your gut flattens the villi, which reduces their ability to help with digestion.

As a result, your intestine is no longer able to digest nutrients from your food, leading to the symptoms of coeliac disease.

Increased risk

It is not known exactly why people develop coeliac disease, or why some have mild symptoms while others have severe symptoms.

However, the below factors are known to increase your risk of developing coeliac disease.

Family history

Coeliac disease often runs in families. If you have a close relative with the condition, such as a parent or sibling, your chance of developing it is higher.

This risk is approximately 10% for those with a family history. If you have an identical twin with coeliac disease, there is a 75% chance you will also develop the condition.

Research shows coeliac disease is strongly associated with a number of genetic mutations (abnormal changes to the instructions that control cell activity) that affect a group of genes called the HLA-DQ genes. HLA-DQ genes are responsible for the development of the immune system and may be passed down through a family.

However, mutations in the HLA-DQ genes are common and occur in about one-third of the population. This suggests that something else, such as environmental factors, must trigger coeliac disease in certain people.

Environmental factors

It is thought environmental factors, including an infection of the digestive system (such as a rotavirus infection) during early childhood, play a part in developing coeliac disease.

There is evidence introducing gluten into your baby's diet before they are three months old may increase their risk of developing coeliac disease.

Most experts recommend you wait until your child is at least six months old before giving them food containing gluten.

There might also be an increased chance of babies developing coeliac disease if they are not being breastfed when gluten is introduced into the diet.

The Food Standards Agency website has more information about introducing gluten into an infant's diet.

Other health conditions

A number of other health conditions can increase your risk of developing coeliac disease. Health conditions associated with coeliac disease include:

• type 1 diabetes
• ulcerative colitis – a digestive condition that causes inflammation of the colon (large bowel)
• neurological disorders (which affect the brain and nervous system) such as epilepsy

See diagnosing coeliac disease for a more extensive list of conditions associated with coeliac disease.

It is unclear whether these health conditions are independent risk factors for developing coeliac disease, or whether they and coeliac disease are both caused by another, single underlying cause.