Ulcerative colitis (UC) is a form of irritable bowel disease (IBD). It causes inflammation in the large intestine, which is called the colon.

Here are 12 facts you might not know about UC and the people who have it.

1. It only affects the lower intestine

Confusing ulcerative colitis with Crohn’s disease is common. They’re both types of IBD that affect the GI tract. And they both share symptoms like cramps and diarrhea.

One way to tell the difference is by the location. UC is confined to the inner lining of the colon. Crohn’s can be anywhere in the GI tract, from mouth to anus.

2. Just under 1 million Americans have UC

About 907,000 American adults live with this condition, according to the Crohn’s & Colitis Foundation.

3. It affects younger and older adults

Most often, UC is diagnosed in people between the ages of 15 and 30, or after the age of 60.

4. Appendix surgery might help some people avoid UC

People who get their appendix removed may be protected from UC, but only if they have the surgery early in life. Researchers don’t know the exact link between the appendix and IBD. It may have to do with the role the appendix plays in the immune system.

5. It runs in families

Between 10 and 25 percent of people with UC have a brother, sister, or parent with the disease. Genes play a role, but researchers haven’t pinpointed which ones are involved.

6. It’s not just about the colon

UC can also affect other organs. About 5 percent of people with IBD will develop severe inflammation in their liver. UC medications also treat disease in the liver.

7. Symptoms differ from person to person

Diarrhea, cramps, and bleeding are typical UC symptoms. Yet they can differ in intensity from mild to moderate to severe. Symptoms also come and go with time.

8. Medication won’t cure the disease

None of the medications used to treat UC cure the disease, but they can manage its symptoms and increase the length of symptom-free periods called remissions. The only way to truly cure UC is with surgery to remove the colon and rectum.

9. There is no “ulcerative colitis diet”

No single food or combination of foods treats UC. Yet some people find that certain foods aggravate their symptoms. If you notice that foods like dairy, whole grains, or artificial sweeteners make your symptoms worse, try to avoid them.

10. UC increases your risk of getting colon cancer

Having UC increases your risk of getting colorectal cancer. Your risk starts to increase after you’ve had the disease for eight to 10 years.

But your chances of actually getting this cancer are still slim. Most people with ulcerative colitis won’t get colorectal cancer.

11. Surgery is a possibility

Between 23 and 45 percent of people with ulcerative colitis will eventually need surgery. Either medication isn’t effective for them, or they’ll develop complications like a hole in the colon that need to be fixed.

12. Celebrities get UC, too

Actress Amy Brenneman, former White House Press Secretary Tony Snow, and Japanese Prime Minister Shinzō Abe are among the many famous people who’ve been diagnosed with UC.