Crohn's Disease

What happens in Crohn's disease

In Crohn's disease, the immune system reacts abnormally to gut bacteria in genetically susceptible people. Inflammation develops in patches ("skip lesions"), with healthy bowel in between. It can involve the full thickness of the bowel wall (transmural inflammation), which explains its complications:

• strictures: scarring narrows the bowel and can block it
• fistulas: tunnels from the bowel to other organs or the skin
• abscesses: pockets of infection

Where Crohn's occurs

Symptoms

Digestive symptoms

• diarrhea, often for weeks, sometimes with blood if the colon is involved
• cramping belly pain, often in the lower right, worse after eating
• urgency and feeling of incomplete emptying
• perianal pain, discharge or swelling from fissures, fistulas or abscesses
• mouth ulcers
• nausea, bloating and loss of appetite

Whole-body symptoms

• fatigue, often profound
• weight loss and malnutrition
• fever during flares
• anemia from blood loss and poor iron absorption
• in children: slowed growth and delayed puberty

Symptoms outside the gut

• joints: arthritis of large joints or the spine. See enteropathic arthritis.
• eyes: red, painful eyes (episcleritis, uveitis)
• skin: tender red nodules on the shins (erythema nodosum), pyoderma gangrenosum ulcers
• liver and bile ducts: primary sclerosing cholangitis, less commonly than in ulcerative colitis
• kidney stones and gallstones, from fat malabsorption
• bone thinning and blood clots

Crohn's disease vs ulcerative colitis

Causes and risk factors

The exact cause is unknown. Contributors include:

• genetics: more than 200 gene variants are linked to IBD, including NOD2. Having a parent or sibling with IBD raises risk.
• gut microbiome: an altered balance of gut bacteria
• immune dysregulation
• smoking: doubles the risk and makes Crohn's more aggressive
• NSAIDs can trigger flares
• urban living, a Western diet and antibiotic exposure in childhood are associated with higher risk

Stress and diet do not cause Crohn's, though they can influence symptoms.

Diagnosis

• Blood tests: blood count, iron, B12, vitamin D, CRP, albumin and liver tests.
• Stool tests: fecal calprotectin, a marker of bowel inflammation that helps tell IBD from irritable bowel syndrome, and tests to exclude infection, including C. difficile.
• Colonoscopy with ileoscopy and biopsies: the key test. It shows ulcers, cobblestoning and skip lesions, and biopsies may show granulomas.
• Small bowel imaging: MRI enterography or CT enterography, or capsule endoscopy.
• Upper endoscopy if upper symptoms are present.
• Pelvic MRI for perianal fistulas.

Treatment

The goal is not just to relieve symptoms but to heal the bowel lining (mucosal healing), which lowers the risk of complications and surgery. Doctors increasingly start effective therapy early in people with moderate to severe disease rather than stepping up slowly.

Treating flares

• corticosteroids (prednisone, or budesonide for ileal disease) for short-term control. They are not used long-term because of side effects.
• exclusive enteral nutrition, a liquid formula diet for 6 to 8 weeks, which is first-line for children
• antibiotics for abscesses and some perianal disease

Long-term (maintenance) treatment

• anti-TNF biologics: infliximab, adalimumab, certolizumab
• anti-integrin: vedolizumab
• anti-IL-12/23 and anti-IL-23: ustekinumab, risankizumab, guselkumab, mirikizumab
• JAK inhibitor: upadacitinib
• immunomodulators: azathioprine, 6-mercaptopurine or methotrexate, alone or with a biologic
• 5-ASA drugs (mesalamine), widely used in ulcerative colitis, have little benefit in Crohn's

Biologics and immune-suppressing drugs increase infection risk. Screening for tuberculosis and hepatitis B before starting, and keeping vaccines up to date, are essential.

Surgery

About half of people with Crohn's need surgery at some point, most often to remove a narrowed or damaged segment, drain abscesses or treat fistulas. Surgery does not cure Crohn's, and inflammation often returns near the join, so medication usually continues afterward.

Nutrition and diet

There is no single Crohn's diet. Helpful approaches:

• a balanced diet to prevent malnutrition, with a dietitian's input
• during flares or with strictures, a low-fiber, low-residue diet to reduce blockage risk
• small, frequent meals
• limiting foods that personally trigger symptoms, such as greasy, spicy or very high-fiber foods
• correcting iron, B12, vitamin D and calcium deficiencies
• structured diets such as the Crohn's disease exclusion diet may help some people under supervision

Complications

• bowel obstruction from strictures
• fistulas and abscesses
• malnutrition, anemia and growth failure
• colorectal cancer risk when the colon is involved for many years, so surveillance colonoscopies start about 8 years after diagnosis
• blood clots, osteoporosis and infections linked to treatment
• short bowel syndrome after extensive surgery

Living with Crohn's

• stop smoking: the single most effective lifestyle change
• avoid NSAIDs such as ibuprofen when possible; acetaminophen (paracetamol) is safer for pain
• take maintenance medicines even when well
• plan pregnancy during remission. Most IBD medicines are safe to continue in pregnancy, but methotrexate is not
• get support for fatigue, anxiety and depression, which are common
• know where restrooms are, and use workplace or school accommodations if needed

Frequently asked questions

What are the first signs of Crohn's disease?

Early signs often include diarrhea lasting weeks, cramping belly pain (often in the lower right), fatigue, weight loss, and sometimes fever, mouth ulcers or problems around the anus such as fissures or fistulas. Children may grow more slowly.

What causes Crohn's disease?

Crohn's results from an abnormal immune response to gut bacteria in people with a genetic predisposition. Smoking, certain medicines such as NSAIDs, and environmental factors increase risk. It is not caused by stress or a particular food, though both can affect symptoms.

What triggers a Crohn's flare?

Common triggers include stopping or missing medicines, smoking, NSAIDs, infections including gut infections, and sometimes antibiotics. Stress and certain foods can worsen symptoms in some people. Sometimes no trigger is found.

Is there a cure for Crohn's disease?

There is no cure yet, but treatment can control inflammation and keep many people in remission for years. Biologic and small-molecule drugs can heal the bowel lining and reduce complications. Surgery can remove damaged sections but does not cure the disease.

What is the best diet for Crohn's disease?

No single diet suits everyone. A balanced diet that maintains weight and nutrients is key. During flares, or with narrowed bowel, a low-fiber diet can reduce pain and blockage risk. A dietitian can help identify personal triggers and correct deficiencies.

What is the difference between Crohn's disease and ulcerative colitis?

Both are inflammatory bowel diseases. Crohn's can affect any part of the gut in patches and through the full thickness of the wall, causing strictures and fistulas. Ulcerative colitis affects only the colon's inner lining continuously from the rectum, and removing the colon cures it.