Coeliacs suffer from an autoimmune disease, the effects of which mean that the intake of gluten is dangerous.
Malorie Knoester, from the Coeliac Society of Ireland, explained that, when a coeliac eats gluten, it causes the body's immune system to turn on itself.
In some cases people with the disease suffer immediate symptoms from eating gluten, which is the name for the proteins found in wheat, rye, barley and some other grains.
However, in others the symptoms can be delayed, while people can be coeliac without even knowing it.
"When a coeliac eats gluten, it causes their immune system to attack the villi in the small intestine," Ms Knoester said. "Essentially it means that the body is fighting itself."
Villi line the small intestine and are responsible for absorbing nutrients in the body. For this reason, coeliacs can suffer from nutrient deficiencies following damage to the villi.
"There is no cure, so a coeliac has to have a strict, gluten-free diet for life," Ms Knoestar said.
"It goes to show the importance of labelling. Remember, there's a difference between people who choose not to eat gluten as part of their diet and coeliacs, who can't."
Diarrhoea, stomach pains and nausea are among the symptoms that someone with the disease can suffer after eating gluten.
More serious problems can occur, including fertility issues in women and anaemia.
It can also cause psychological effects, from irritability to depression.
"Even a small amount of gluten is very dangerous and can be very damaging," Ms Knoester added.