Causes and Risk Factors of Inflamed Colon

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The colon is the longest part of the large intestine, where water and some nutrients are absorbed from food waste as it passes through. The colon can become inflamed in response to injury or illness. This inflammation is called colitis and can cause abdominal pain, cramping, and diarrhea.

The inflammation can either be a short-term or a long-term problem. Colitis could be caused by:

  • An allergic reaction
  • An infection
  • Ischemic colitis (decreased blood flow)
  • Medications
  • Inflammatory bowel disease (IBD)
  • Microscopic colitis

This article will explore the common causes, genetics, and lifestyle risk factors for an inflamed colon.


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Common Causes

Colitis can result from acute (sudden and short-term) illness or chronic (long-term) illness.


One common cause of inflammation in the colon is an infection by a virus, bacterium, or parasite. This is sometimes called infectious colitis.

Food poisoning is an illness that can cause acute colon inflammation. It occurs after contact with contaminated food or water. Some common bacteria that cause food poisoning include campylobacter, Escherichia coli (E. coli), salmonella, and shigella. Other types of bacteria may also cause colitis.

Parasites can also be responsible for an infection in the colon. A parasite that is commonly involved is called Giardia lamblia. The infection can be foodborne (originating from contaminated food or water) or it can come from contact with the stool of someone who is infected (called the fecal-oral route).

Another bacterium that can cause colitis is Clostridium difficile, also known as C. difficile or C. diff. It is normally found in the colon, but it can grow out of control under certain conditions. This can happen after taking antibiotics, which causes disruption in the bacterial balance in the colon.

C. diff infection is highly contagious, and it can easily be passed from person to person in settings such as hospitals or long-term care centers.

Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) has three common types: Crohn's disease, ulcerative colitis, and indeterminate colitis. All forms of IBD cause inflammation in the digestive tract, with ulcerative colitis and indeterminate colitis being largely confined to the colon.

In Crohn's disease, inflammation can occur anywhere in the digestive system, but when it is only found in the colon, it is known as Crohn's colitis.

IBD is common in developed nations and becoming more so in other parts of the world. The signs and symptoms can include bloody diarrhea, pain, weight loss, anemia, and many other potential problems outside of the digestive tract.

Treatment can include one or more of many classes of medications, including aminosalicylates, biologics, immune-modifying drugs, Janus kinase (JAK) inhibitors, and steroids. Surgery to remove part or all of the colon is another possible treatment. Surgery is more common in Crohn's disease than ulcerative colitis.

Ischemic Colitis

In ischemic colitis, the arteries that send blood to the colon can narrow. This narrowing can happen if the bowel gets twisted, cutting off blood flow, or from a blood clot that blocks an artery.

There are many causes of reduced blood flow to the colon, including anemia, dehydration, low blood pressure, and shock. The symptoms of ischemic colitis can include bloody stools, fever, and severe pain.

When blood flow is cut off or reduced, colon tissue may begin to die. Hospitalization may be required to correct the problem, and surgery may be necessary in some cases.

Some of the risk factors for ischemic colitis are:


Some medications may cause bleeding and/or inflammation in the colon. The most common of these are nonsteroidal anti-inflammatory medications (NSAIDs), such as ibuprofen or aspirin.

Taking methotrexate, which is used to treat several autoimmune or immune-mediated conditions, may also contribute to colitis. Sodium phosphate, which is a type of laxative, can cause colitis in some cases, as can certain forms of chemotherapy (drugs used to treat cancer).

Allergic Colitis

Newborns and infants are most commonly affected by colon inflammation that's caused by an allergy. However, older children can also get colitis in this way. Cow's milk is the most common cause of allergic colitis in babies.

One of the symptoms can be blood in the stool, which is distressing to parents. Usually, treatment involves starting a diet that removes potential allergens. Most cases will resolve as the baby gets older.

Microscopic Colitis

There are two types of microscopic colitis, which are lymphocytic colitis and collagenous colitis. Microscopic colitis often causes chronic diarrhea.

These conditions are substantially more common in women than in men, although some studies have shown lymphocytic colitis may be more common in men than previously thought. Microscopic colitis can happen at any age but is more common in people in their 60s and 70s.

Treatment will depend on how severe the symptoms are and can include aminosalicylates, bismuth subsalicylate (Pepto Bismol), steroids, and/or immune-modifying drugs.


Many of the causes of colon inflammation don't seem to have a genetic component. It's still important to keep track of the diseases and conditions that run in your family and let healthcare professionals know about them.

IBD is one form of colitis that does seem to run in families. Although there is not always a direct parent-to-child link, first-degree relatives of someone with IBD, including parents and siblings, are more likely to also have the disease.

IBD is thought to have both a genetic and an environmental component, however. Not everyone who has the genes associated with IBD eventually develops the disease.

It's important to tell healthcare professionals if any relatives have ever been diagnosed with IBD.

Lifestyle Risk Factors

The causes of colon inflammation are extremely varied, and tie-ins to lifestyle will differ based on each condition. However, using NSAIDs long term and smoking cigarettes can result in colitis.

Infectious causes of colitis can be prevented by avoiding untreated water sources and being strict in handling, preparing, and storing food safely.

Proper nutrition is important for everyone, and in some cases, it may be necessary to change your diet to help address colon inflammation. A dietitian can help you understand whether the foods you eat are contributing to your colon inflammation and how to eliminate certain foods (such as with allergic colitis).


Colon inflammation, or colitis, can be acute (short-lived), or it can be chronic (long term). Foodborne illnesses and infections are common causes of acute colitis. Ischemic colitis is a serious acute condition occurring when blood flow to the colon is blocked.

Chronic forms of colitis include inflammatory bowel disease, allergic colitis, and microscopic colitis. Using medications such as NSAIDs and methotrexate may also result in colon inflammation.

A Word From Verywell

An inflamed colon can cause bloody stools. Blood in or on the stool is never normal and should always be a reason to see a doctor. Seek medical attention right away when you experience severe pain, bleeding with clots, persistent heavy diarrhea, or constipation that doesn't go away.

It may take time to properly diagnose the reason for your colon inflammation because there are so many potential causes. But a healthcare professional can help you discover the reason for your symptoms and prescribe the proper treatment.

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8 Sources
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