Introduction to IBD.
The basics of Crohn’s disease and ulcerative colitis: what they are, how doctors diagnose them, and why you are not alone.
Lesson 1 of 5
3 min read · Updated September 16, 2026 · Medically reviewed by Shamita Shah, MD
In this lesson
Key takeaways
- IBD includes Crohn’s disease and ulcerative colitis. Both cause long-term inflammation in the gut.
- No single test diagnoses IBD. A colonoscopy with biopsies confirms it.
- IBD can affect your joints, skin, eyes or liver, not just your gut.
- With the right care team and treatment, most people with IBD live full, active lives.
What is IBD?
Inflammatory bowel disease (IBD) is a condition of the immune system. It includes ulcerative colitis (UC) and Crohn’s disease (CD). Both are long-term (chronic) conditions that cause swelling and irritation of the lining of the gut. Doctors call this inflammation. If it isn’t treated, inflammation can lead to complications.
How IBD is diagnosed
There is no single test for IBD. Instead, doctors use several tools to build a clear picture. The process usually starts with your medical history and a physical exam.
Blood and stool tests come next. Some of these tests look for signs of active inflammation, called biomarkers, and can be repeated over time to see how well treatment is working. Examples include blood tests for anemia or for CRP (an inflammation marker), and a stool test called fecal calprotectin. If you have diarrhea, a stool test can also rule out an infection.
These tests can’t confirm IBD on their own, but they help your doctor decide whether you need more testing. The test that confirms IBD is a colonoscopy. The doctor uses a thin, flexible tube with a camera to look at the lining of your intestine and take small tissue samples (biopsies).
Crohn’s disease
Crohn’s disease can cause inflammation anywhere along the digestive tract, from the mouth to the anus. It most often affects the end of the small intestine (the ileum) and the start of the colon. A key feature of Crohn’s is that the inflammation can go through the full thickness of the intestinal wall, not just the surface. Doctors call this “transmural.”
Ulcerative colitis
Ulcerative colitis causes ongoing inflammation, with sores and ulcers, in the large intestine only. It affects the inner surface lining of the intestine.
Symptoms beyond the gut
Many people think IBD only affects the gut. In fact, 25 to 40 percent of people with IBD also have inflammation in the joints, skin, eyes or liver. People with IBD may also have fatigue, body pain and fevers.
You are not alone
More than 7 million people around the world live with IBD, and that number has risen steadily for decades. In the United States, about 2.4 to 3.1 million adults live with Crohn’s disease or ulcerative colitis. IBD can start at any age and affects men and women equally.
There is no cure for Crohn’s disease. For ulcerative colitis, surgery to remove the entire colon is the only cure. The goal of IBD care is remission, so you can enjoy a normal quality of life and avoid complications. With the right care team and treatment plan, people with IBD can live full, active lives.
Whatever your age or background, many others share your experience with IBD, and dedicated communities and specialists are here to help.
Questions to ask at your next visit
- Do I have Crohn’s disease or ulcerative colitis? Which part of my gut is affected?
- Which tests will I need, and how often?
- What is the goal of my treatment plan?
- What changes in my symptoms should I tell you about right away?
Who to call
Medical emergency
Call 911 or go to the nearest emergency room.
Symptoms or medicine questions
Contact your GI doctor’s office.
Questions about SonarMD
Call a care coordinator at 312-283-0601, Monday–Friday, 8 a.m.–5 p.m. CT.
This information is for education only and does not replace advice from your doctor. If you have severe symptoms, contact your doctor right away. In an emergency, call 911.