Crohn's disease is a long-term condition where your immune system attacks your digestive tract
Crohn's disease is an inflammatory bowel disease (IBD) that causes your immune system to mistakenly attack the lining of your digestive system. This attack creates inflammation—swelling and irritation—that can occur anywhere from your mouth to your anus, though it most commonly affects the end of your small intestine and the beginning of your large intestine. The inflammation damages the intestinal lining, which leads to the symptoms people experience: abdominal pain, diarrhea, weight loss, and fatigue.
Unlike some digestive conditions that come and go, Crohn's is chronic, meaning it lasts a long time. Most people have periods when symptoms flare up (get worse) and periods of remission (when symptoms improve or disappear). There is no cure, but treatments can control the inflammation and help you feel better.
Key Takeaways
- Crohn's disease happens when your immune system attacks the lining of your digestive tract, causing inflammation that damages the intestines.
- The condition most often affects the junction between your small and large intestines, but can occur anywhere in your digestive system.
- Doctors do not fully understand why some people develop Crohn's, but genetics, immune system function, and environmental factors all play a role.
- Symptoms include abdominal pain, chronic diarrhea, weight loss, and fatigue, and they come and go in cycles of flares and remission.
- A blood test, stool test, or imaging scan can help doctors diagnose Crohn's, but a biopsy (tissue sample) from the intestines is often needed to confirm it.
How the immune system causes inflammation in Crohn's disease
Your immune system normally protects you by attacking harmful bacteria and viruses. In Crohn's disease, something goes wrong with this system. Your immune cells begin to treat the bacteria and other organisms that live naturally in your gut as invaders and attack them. This triggers a chain reaction: your immune system releases chemicals that cause inflammation, the intestinal lining swells and becomes damaged, and the damaged tissue stops working properly.
When the intestinal lining is damaged, it becomes harder for your body to absorb nutrients from food, and it becomes easier for bacteria and partially digested food to irritate the tissue further. This creates a cycle where inflammation leads to more damage, which leads to more inflammation. The damaged areas can develop ulcers (open sores) and scarring, which can narrow the intestines and make it harder for food to pass through.
Why some people develop Crohn's disease
Doctors do not yet fully understand what causes Crohn's disease, but research shows that three main factors are involved: your genes, your immune system, and your environment. These factors interact in ways scientists are still studying.
Genetics play a significant role. If a close family member has Crohn's disease, your risk of developing it is higher than someone with no family history. However, having a family member with Crohn's does not mean you will definitely get it—many people with a genetic risk never develop the disease. Researchers have identified more than 200 genetic variations linked to Crohn's, but no single gene causes it.
Immune system differences are another piece. People with Crohn's have immune systems that respond differently to bacteria in the gut. Some research suggests their immune systems overreact to normal gut bacteria, while other research points to problems with immune cells that normally keep inflammation in check. The exact mechanism is still being investigated.
Environmental factors also matter. These include diet, stress, smoking, infections, and antibiotics you may have taken. For example, smoking increases the risk of developing Crohn's and makes symptoms worse. Some studies suggest that a diet high in processed foods and low in fiber may increase risk, though the evidence is still developing. Early childhood infections or the use of antibiotics that disrupt your gut bacteria may also play a role, though researchers are still working out the details.
Where Crohn's disease develops in your digestive system
Crohn's disease can affect any part of your digestive tract from your mouth to your anus, but it most commonly occurs in the terminal ileum—the last part of your small intestine—and the colon (large intestine). About half of people with Crohn's have inflammation in both of these areas.
The location of inflammation matters because it affects which symptoms you experience and how your body absorbs nutrients. If inflammation is in your small intestine, you may have more trouble absorbing vitamins and minerals, leading to deficiencies. If it is in your colon, you are more likely to have bloody diarrhea. Some people have inflammation in just one spot, while others have multiple areas of inflammation with normal tissue in between—a pattern doctors call "skip lesions."
Symptoms that signal Crohn's disease
The symptoms of Crohn's disease vary from person to person and depend on where the inflammation is located and how severe it is. The most common symptoms are abdominal pain and cramping, chronic diarrhea (lasting more than a few weeks), blood in your stool, weight loss, and fatigue. Some people also experience fever, joint pain, or skin problems.
Symptoms often come in cycles. During a flare, symptoms worsen and may be severe enough to interfere with daily life. During remission, symptoms improve or disappear entirely, sometimes for months or even years. The unpredictability of these cycles is one reason Crohn's can be challenging to live with—you may feel well one week and very ill the next.
It is important to know that Crohn's disease affects more than just your digestive system. Inflammation from Crohn's can cause problems in other parts of your body, including your joints, eyes, skin, and liver. These are called extraintestinal manifestations, and they occur in about one-third of people with Crohn's.
How doctors diagnose Crohn's disease
If your doctor suspects Crohn's disease based on your symptoms, they will order tests to confirm the diagnosis. There is no single test that definitively diagnoses Crohn's, so doctors use a combination of approaches.
Blood tests can show signs of inflammation (elevated C-reactive protein or erythrocyte sedimentation rate) and check for anemia or nutritional deficiencies. Stool tests can rule out infections that cause similar symptoms. Imaging studies like CT scans or MRI can show inflammation and damage in your intestines. Colonoscopy—a procedure where a camera on a thin tube is inserted through your colon—allows your doctor to see the intestinal lining directly and take small tissue samples (a biopsy). The biopsy is often the key to confirming Crohn's disease because it shows the specific pattern of inflammation that doctors look for.
Your doctor may also perform an upper endoscopy, which is similar to a colonoscopy but examines your upper digestive tract instead. This helps determine how far up your digestive system the inflammation extends.
The difference between Crohn's disease and ulcerative colitis
Crohn's disease and ulcerative colitis are both inflammatory bowel diseases, and they share many symptoms, but they are different conditions. The main difference is location and depth of inflammation. Crohn's can occur anywhere in the digestive tract and affects all layers of the intestinal wall. Ulcerative colitis occurs only in the colon and rectum and affects only the innermost lining.
This difference matters for treatment. Some medications work for both conditions, but others are specific to Crohn's. Your doctor will determine which condition you have through testing, and that diagnosis will guide your treatment plan.
Frequently Asked Questions
Is Crohn's disease contagious?
No, Crohn's disease is not contagious. You cannot catch it from someone else, and you cannot pass it to others. It is an autoimmune condition caused by a combination of genetics and immune system factors, not by an infection.
Can children get Crohn's disease?
Yes, Crohn's disease can develop at any age, including childhood. When it occurs in children, it is sometimes called pediatric Crohn's disease. Early diagnosis and treatment are important because untreated inflammation can affect growth and development.
Does diet cause Crohn's disease?
Diet does not cause Crohn's disease, but certain foods can trigger or worsen symptoms in some people. Common trigger foods include high-fiber foods, fatty foods, dairy, and spicy foods, though triggers vary widely. During a flare, a bland diet may help, but there is no universal diet that prevents or cures Crohn's.
Will I need surgery if I have Crohn's disease?
Not everyone with Crohn's needs surgery, but some people do. Surgery may be necessary if medication does not control inflammation, if you develop complications like strictures (narrowed areas) or fistulas (abnormal connections between intestines), or if you have severe bleeding. Your doctor will discuss whether surgery is right for you based on your individual situation.
Can Crohn's disease go away on its own?
Crohn's disease is a chronic condition, meaning it lasts long-term and does not go away on its own. However, periods of remission can last months or years, during which you may have few or no symptoms. Treatment aims to achieve and maintain remission and prevent flares.