Crohn's disease is a long-term condition that causes inflammation of the lining of the digestive system. Inflammation can affect any part of the digestive system, from the mouth to the back passage, but most commonly occurs in the last section of the small intestine (ileum) or the large intestine (colon). Common symptoms can include: diarrhoea abdominal pain fatigue (extreme tiredness) unintended weight loss blood and mucus in your faeces (stools) People with Crohn's disease sometimes go for long periods without symptoms or with very mild symptoms. This is known as remission. Remission can be followed by periods where symptoms flare up and become particularly troublesome.