Ulcerative colitis

Ulcerative colitis is one of the two main forms of inflammatory bowel disease (IBD). It is a long-term condition in which the lining of the colon and rectum, together known as the large intestine, becomes inflamed and develops small open sores called ulcers (NHS; Cleveland Clinic).

One detail sets it apart from Crohn's disease: ulcerative colitis stays in the large intestine only, and the inflammation is continuous rather than patchy. It usually starts in the rectum, close to the anus, and may reach further up the colon. It also affects only the innermost lining of the bowel, not the deeper layers (Cleveland Clinic).

Main symptoms

The most common symptoms are recurring diarrhoea that may contain blood, mucus or pus, abdominal pain or cramping, and needing to empty the bowels more often or more urgently. Tiredness, loss of appetite and weight loss can come with a flare (NHS).

A relapsing pattern

Ulcerative colitis tends to come and go. Many people have weeks or months of very mild symptoms, or none at all, a state called remission, followed by periods when symptoms return and are harder to live with, called flare-ups (NHS).

What causes it

It is thought to be an autoimmune condition, where the immune system mistakes harmless bacteria in the colon for a threat and inflames the lining. Exactly why this happens is not fully understood, and a mix of genetic and environmental factors is thought to play a part. It runs more often in families (NHS; Cleveland Clinic).