What Is Crohn’s Disease? A Nurse Explains the Basics

By Anna Curran, RN, BSN, PHN · Last reviewed October 2026

Crohn’s disease is a long-term condition that causes inflammation in the digestive tract. It is a type of inflammatory bowel disease, or IBD. It can affect any part of the gut from the mouth to the anus, but it most often affects the end of the small intestine and the start of the large intestine.

If you or someone you love was just diagnosed, you probably have a lot of questions. So, what is Crohn’s disease, and what does it mean for daily life? Here is a clear, plain-language look at the basics.

What Is Crohn’s Disease?

In Crohn’s disease, the immune system reacts in an abnormal way. Instead of protecting you, it causes swelling and irritation (inflammation) in the lining and walls of your digestive tract. Over time, this can lead to sores, scarring and other problems.

Crohn’s is chronic, which means it lasts a long time. It often starts slowly and can change over the years. Symptoms can be mild for some people and severe for others.

Most people go through cycles:

Flares are times when symptoms are active.
Remission is a time when symptoms ease or go away. Remission can last weeks or even years.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) estimates that about 1 million people in the United States have Crohn’s disease. The CDC estimates that 2.4 to 3.1 million people in the U.S. have some form of IBD.

Where Crohn’s Disease Can Show Up

Crohn’s can affect any part of the digestive tract. Cleveland Clinic describes several types based on location:

Ileocolitis: the end of the small intestine (the ileum) and the colon. This is the most common type.
Ileitis: only the ileum.
Crohn’s colitis: only the large intestine.
Gastroduodenal Crohn’s: the stomach and the first part of the small intestine.
Jejunoileitis: patchy areas in the upper small intestine.

Where your Crohn’s is located helps explain your symptoms. It also guides which tests and treatments your care team chooses.

Crohn’s vs. Ulcerative Colitis vs. IBS

These three conditions are often confused. They can share some symptoms, like belly pain and diarrhea, but they are not the same.

	Crohn’s disease	Ulcerative colitis	IBS
Type	IBD	IBD	Not IBD
Where	Anywhere from mouth to anus	Only the colon and rectum	Gut function, no damage
Pattern	Patchy, with healthy areas in between	Continuous, starting at the rectum	No inflammation
Depth	Can go through all layers of the bowel wall	Inner lining only	No tissue damage

Because Crohn’s can go deep into the bowel wall, it can cause problems like narrowing, tunnels and pockets of infection. Ulcerative colitis stays in the inner lining of the colon.

Irritable bowel syndrome (IBS) is a different condition. Mayo Clinic explains that IBS causes symptoms like belly pain, bloating and changes in bowel habits, but without inflammation or damage to the gut. It is not a form of IBD.

This difference matters. IBD and IBS are treated in very different ways, so getting the right diagnosis is important.

Who Gets Crohn’s Disease?

Anyone can get Crohn’s disease, at any age and of any race. According to NIDDK, it is more likely in people who:

Are between 20 and 29 years old
Have a parent, brother or sister with IBD
Are of Jewish descent
Smoke cigarettes

Mayo Clinic notes that most people are diagnosed before age 30. It also notes that Crohn’s is becoming more common in groups where it used to be less common, including Black people in North America and people who have moved to the U.S.

What Causes Crohn’s Disease?

Doctors do not know the exact cause. Researchers think it comes from a mix of factors working together:

Immune system: The immune system may attack the normal, helpful bacteria that live in your gut. This sets off inflammation.
Genes: Crohn’s sometimes runs in families.
Gut bacteria: The mix of germs in the gut (the microbiome) looks different in people with IBD. Researchers are still studying what this means.
Environment: Smoking may double the risk of Crohn’s disease, according to NIDDK.

It helps to know what does not cause Crohn’s. You did not cause it by something you ate. The Crohn’s & Colitis Foundation says diet does not cause Crohn’s or ulcerative colitis, though food can affect symptoms. Stress also does not cause IBD, though it can make symptoms feel worse.

Some medicines can make things worse. Mayo Clinic notes that NSAIDs, such as ibuprofen and naproxen, can worsen bowel inflammation. They do not cause Crohn’s. Ask your doctor or pharmacist which pain reliever is safest for you.

Common Symptoms

Symptoms depend on where the inflammation is and how severe it is. The most common are:

Diarrhea
Belly pain and cramping
Weight loss

Other symptoms can include tiredness, fever, low appetite, nausea, blood in the stool, mouth sores, and pain or drainage near the anus. Some people also have problems outside the gut, such as joint pain, red or painful eyes, or red, tender bumps on the skin.

Possible Complications

Crohn’s can cause problems both inside and outside the digestive tract. Knowing them helps you spot changes early.

In the gut:

Strictures: Scarring narrows the bowel, which can lead to a blockage.
Fistulas: Tunnels that form between the bowel and another area, such as the skin or another organ.
Abscesses: Pockets of infection.
Anal fissures: Small tears around the anus.
Ulcers: Sores in the mouth, intestines or around the anus.

In the rest of the body:

Anemia from low iron or low vitamin B12
Malnutrition
Bone loss, which can be related to the disease and to steroid use
Arthritis, skin and eye problems
Liver and bile duct problems
Kidney stones
Slow growth or delayed puberty in children

Crohn’s that affects the colon raises the risk of colorectal cancer. Your doctor will tell you when to start colonoscopy screening. Many people with IBD also deal with stress, anxiety or depression. These are real parts of living with a chronic illness, and they deserve care too.

When to Get Help Right Away

Call 911 or go to the emergency room if you have:

Severe or constant belly pain
Signs of a bowel blockage, such as vomiting, a swollen belly, or not being able to pass gas or stool
Heavy rectal bleeding or blood clots in your stool
Vomiting so much you cannot keep liquids down
A high fever with belly pain

See your doctor soon if you have diarrhea that lasts more than one to two weeks, weight loss without trying, ongoing changes in your bowel habits or blood in your stool.

What Is the Outlook?

There is no cure for Crohn’s disease yet. But there is real reason for hope. Treatment has come a long way, and there are now many medicine options.

Cleveland Clinic notes that Crohn’s usually is not life-threatening and that most people have a normal life expectancy. Most people can live full, active lives with good care.

Treatment aims to calm inflammation, prevent flares and keep you in remission. It may include medicines, nutrition support and sometimes surgery. Staying in touch with your gastroenterologist, taking medicines as prescribed and keeping up with checkups all make a difference.

If you smoke, quitting is one of the most helpful things you can do for your gut. Ask your doctor for help with a plan to quit.

Frequently Asked Questions

Is Crohn’s disease the same as IBS?

No. Crohn’s disease is a type of IBD that causes inflammation and can damage the bowel. IBS causes gut symptoms without inflammation or damage. They are diagnosed and treated differently.

Can Crohn’s disease be cured?

Not yet. There is no cure, but treatment can calm inflammation and help many people reach long periods of remission. Surgery can treat complications, but it does not cure Crohn’s.

Is Crohn’s disease genetic?

Genes play a role, and Crohn’s sometimes runs in families. Having a parent or sibling with IBD raises your risk. But many people with Crohn’s have no family history at all.

Did something I ate cause my Crohn’s?

No. Food does not cause Crohn’s disease. Some foods may bother you more during a flare, and a food journal can help you find your triggers.

The Bottom Line

Crohn’s disease is a chronic type of IBD that causes inflammation anywhere in the digestive tract. It differs from ulcerative colitis in where and how deep it affects the bowel, and it is very different from IBS. The exact cause is unknown, but genes, the immune system, gut bacteria and smoking all play a part. With good treatment and regular care, most people with Crohn’s live full lives and have a normal life expectancy.