The classic clinical presentation in adults with Celiac disease is diarrhea, which may be accompanied by abdominal pain or discomfort. Other silent presentations include iron-deficiency anaemia, osteoporosis, and less common symptoms include constipation, weight loss and dermatitis herpetiformis when gluten containing foods are consumed. Some people may also have had a previous diagnosis of irritable bowel syndrome. When people with celiac disease eat foods or use products containing gluten, their immune system responds by damaging or destroying villi, the tiny, fingerlike protrusions lining the small intestine. Villi normally allow nutrients from food to be absorbed through the walls of the small intestine into the bloodstream, so if these are damaged, mal-absorption can occur.