Colitis can have numerous causes, from infection to inflammatory bowel disease, drug interactions, and allergic reactions.

Colitis is a general term for the inflammation of the colon’s inner lining, which is your large intestine. There are different types of colitis categorized by cause. Infections, poor blood supply, and parasites can all cause an inflamed colon.

If you have an inflamed colon, you’ll likely have abdominal pain, cramping, and diarrhea.

There are a few types of colitis and other conditions that can cause colon inflammation.


Viruses, bacteria, and parasites can cause infectious colitis. A person who has infectious colitis will have diarrhea and fever, and a stool sample that tests positive for enteropathogens such as:

Depending on the cause of the infection, infectious colitis may be contracted from contaminated water, foodborne illnesses, or poor hygiene.

Pseudomembranous colitis is another type of infectious colitis. It’s also referred to as antibiotic-associated colitis or C. diff colitis because it results from an overgrowth of the bacteria Clostridium difficile.

It’s most often caused by antibiotic use that interferes with the balance of healthy bacteria in the colon.

Inflammatory bowel disease (IBD)

According to the Centers for Disease Control and Prevention (CDC), approximately 3 million U.S. adults had IBD as of 2015. IBD is a group of chronic diseases that cause inflammation in the digestive tract. Many conditions fall under the IBD umbrella, but the two main types are:

Crohn’s disease

Crohn’s disease causes inflammation of the lining of the digestive tract. Any part of the digestive tract can be affected, but it most often develops in the ileum, the last part of the small intestine.

Early symptoms of Crohn’s disease may develop slowly over time and some may become worse. These symptoms can include:

Treatment usually includes anti-inflammatory drugs, immunomodulators (drugs that affect the immune system), antibiotics, or biologics (engineered medicines that target certain proteins or genotypes that cause inflammation).

Ulcerative colitis

This causes chronic inflammation and ulcers in the innermost lining of the colon and rectum. People with ulcerative colitis have an increased risk for colon cancer.

Some of the most common symptoms of ulcerative colitis are:

  • abdominal pain and more than usual abdominal noises
  • bloody stool
  • diarrhea
  • fever
  • rectal pain
  • unexplained weight loss
  • malnutrition

Ulcerative colitis is a chronic condition and treatment is intended to reduce flare-ups. Treatment options can be similar to Crohn’s disease. These may include anti-inflammatory medications, biologics, and immunomodulators.

Surgery may be an option with debilitating symptoms, a perforation of your colon, or severe blockages.

Ischemic colitis

Ischemic colitis occurs when there’s reduced blood flow to a portion of the colon. This stops the cells in your digestive system from getting the oxygen they need.

It’s usually caused by narrowed or blocked arteries. People age 60 or older, have IBS, cardiovascular disease, diabetes mellitus, or a clotting disorder may have an increased risk of ischemic colitis.

Ischemic colitis can affect any part of your colon, but you usually feel pain on the left side of the abdomen. It can occur gradually or suddenly.

Symptoms on your right side may indicate blocked arteries to your small intestine that can quickly cause necrosis of intestinal tissue. This is life-threatening and requires urgent surgery to clear the blockage and remove the damaged portion.

If you feel severe pain on the right side of your abdomen, don’t delay in getting emergency medical care.

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Allergic reactions

Allergic colitis is more common in babies than adults and can be temporary. The inflammation is an allergic reaction to the proteins found in cow’s milk. A baby with an inflamed colon may be irritable, gassy, and have blood or mucus in their stools. Anemia and malnutrition are also possible.

Eosinophilic colitis is similar to allergic colitis. When it occurs in an infant, it usually resolves by early childhood. In adolescents and adults, the condition is often chronic.

The exact cause of eosinophilic colitis isn’t always known, though proteins in cow’s milk often make symptoms worse. People with a personal or family history of allergies and asthma appear to have a higher risk.

Microscopic colitis

Microscopic colitis can be seen only through a microscope. It’s characterized by an increase in lymphocytes, which are a type of white blood cell, in the lining of the colon.

There are two types of microscopic colitis, and though both show an increase in lymphocytes, each type affects the tissue of your colon differently:

  • Lymphocytic colitis has a higher number of lymphocytes, and the tissues and lining of the colon are of normal thickness.
  • In collagenous colitis, the layer of collagen under the lining of the colon is thicker than normal.

The cause of microscopic colitis is unknown, but researchers believe it may be linked to:

  • autoimmune diseases
  • certain medications
  • infections
  • genetics

The symptoms of this type of colitis often come and go, sometimes disappearing without treatment.

Drug-induced colitis

Certain medications, mainly nonsteroidal anti-inflammatory drugs (NSAIDs), have been linked to the inflamed colon in some people. Older people and people with a history of long-term use of NSAIDs appear to be at the highest risk of developing this type of colitis.

Even though there are different types of colitis with different causes, most of the symptoms are the same:

  • diarrhea with or without blood
  • abdominal pain and cramping
  • fever
  • urgency to have a bowel movement
  • nausea
  • bloating
  • weight loss
  • fatigue

Treatment for colitis may vary depending on the cause. If it’s caused by an allergy to a certain food or side effect from a drug, your doctor will recommend removing the food from your diet or changing medication.

Most types of colitis are treated using medication and changes to diet. The goal of treatment for colon inflammation is to reduce the inflammation-causing symptoms.

Medications used to treat colitis may include:

The following lifestyle changes may help relieve your symptoms:

  • keep track of and avoid foods that trigger or worsen your symptoms
  • consider eating smaller, more frequent meals throughout the day
  • avoid foods that increase stool output, such as caffeine and raw fruits and vegetables
  • consider limiting alcohol consumption
  • if you smoke, consider quitting; a doctor can help you create a plan that’s right for you

Surgery may be recommended if other treatments aren’t able to relieve your symptoms or if you have severe damage to your colon.

Chronic diarrhea, severe abdominal pain, or blood in your stool should be evaluated by a doctor. Severe abdominal pain that comes on suddenly and makes it difficult for you to get comfortable may be a sign of a serious condition that requires emergency medical treatment.

The symptoms of colitis can cause discomfort that impacts your quality of life. There are treatment options that can help. Speak with your doctor to find out the best way to treat your symptoms.