Crohn's disease vs ulcerative colitis: how the two main types of IBD differ

Crohn's disease and ulcerative colitis are different diagnoses within the same group of conditions, inflammatory bowel disease. They share a great deal: an overactive immune response that inflames the bowel, flare-ups followed by quieter periods, similar medicines and a lifelong need for follow-up. What mainly separates them is the pattern of inflammation. Crohn's disease can appear in any part of the digestive system and can involve the full thickness of the bowel wall. Ulcerative colitis is confined to the large bowel and rectum.

That distinction matters in practice because it influences which complications a person is watched for, which operations are possible and what the long-term outlook looks like. It is also the reason a specialist will usually want a camera test and tissue samples rather than relying on symptoms alone.

The NHS lists three main types of IBD and describes them by location. Crohn's disease can cause ulcers and inflammation anywhere from the mouth to the bottom. Ulcerative colitis causes ulcers and inflammation in the rectum and large bowel (colon). Microscopic colitis, the third type, causes inflammation in the large bowel.

Crohn's and Colitis UK adds detail. In Crohn's, any part of the gut can be involved, but it will not be everywhere, and it is most common in the small bowel and colon. Areas of inflammation are often patchy, with healthy gut between them. The inflammation can affect all layers of the bowel wall, and if it passes through the middle and outer layers an abscess or fistula may develop. In ulcerative colitis, the charity says the condition usually begins in the rectum and lower colon, though it may involve all of the large bowel.

Because both conditions inflame the bowel, the symptom lists look alike. The NHS names diarrhoea, stomach pain, blood or mucus in the poo, tiredness and weight loss for Crohn's, and diarrhoea (which may contain blood, mucus or pus), tummy pain, needing to poo urgently or during the night, bleeding from the bottom, bloating and tiredness for ulcerative colitis.

The differences are of emphasis rather than kind. The NHS notes that Crohn's symptoms vary depending on which part of the gut is affected, and that in children it can cause poor growth or delayed puberty. Pain around the anus is listed for Crohn's. For ulcerative colitis the NHS highlights lower-left tummy pain that may ease after pooing, frequent or urgent trips to the toilet, and a feeling of needing to go even when the bowel is empty. In both conditions, symptoms may also appear outside the gut, such as joint pain, sore eyes and skin rashes.

Neither list can be used to diagnose yourself. The NHS explicitly says not to try to diagnose the problem yourself, because the symptoms resemble irritable bowel syndrome, diverticular disease and coeliac disease.

There is no single test for Crohn's disease, and the NHS says diagnosis often takes time because symptoms vary and resemble other conditions. A GP may arrange blood tests and a poo sample, and referral to a hospital specialist follows for a camera test through the bottom or throat, tissue samples (biopsy) and scans such as MRI, CT or ultrasound. Ulcerative colitis is also usually diagnosed in hospital by a gastroenterologist using blood tests, a stool sample, scans and a colonoscopy with a biopsy of the bowel lining.

The combination of where the inflammation is, how it looks through the camera and what the biopsy shows is what lets the specialist label the disease. When the inflammation is confined to the colon and these features do not point clearly one way, Crohn's and Colitis UK says the diagnosis may be IBD-U. The charity also says that as many as 1 in 10 people diagnosed with ulcerative colitis will have the diagnosis changed to Crohn's or IBD-U in the first five years, so a first label is not always final.

Medicines overlap heavily. For both conditions the NHS lists steroids to calm a flare-up, mesalazine or sulfasalazine to reduce inflammation, immunosuppressants and biological or targeted medicines. Crohn's can also be treated with a special liquid diet (enteral nutrition) in some people, particularly children or those who cannot take steroids.

Surgery is where the two diverge. In Crohn's, an operation removes the damaged section and joins healthy gut together, or creates a stoma, but the NHS warns symptoms may return elsewhere in the gut. In ulcerative colitis, removing the large bowel (colectomy) stops the disease from coming back, though it means the body needs a different way to pass stool, either an ileostomy or an internal pouch. Each of these decisions sits with a specialist team, and the NHS says your care team will go through benefits and risks with you.

The NHS advises seeing a GP if you think you could have either condition. It advises asking for an urgent GP appointment or contacting NHS 111 for black or dark red poo or bloody diarrhoea in Crohn's, and for very bad or bloody diarrhoea, a high temperature, a fast heartbeat or being unable to pass wind or poo in ulcerative colitis. Call 999 or go to A&E for severe tummy pain, non-stop bleeding from the bottom, a lot of blood or large clots, or vomiting blood or sick that looks like coffee grounds.