Crohn's disease affects the thickness of the intestinal wall. Over time, parts of the bowel can thicken and narrow, which may block the flow of digestive contents through the affected part of your intestine. Some cases require surgery to remove the diseased portion of your bowel.
Ulcers. Chronic inflammation can lead to open sores (ulcers) anywhere in your digestive tract, including your mouth and anus, and in the genital area (perineum) and anus.
Fistulas. Sometimes ulcers can extend completely through the intestinal wall, creating a fistula — an abnormal connection between different parts of your intestine, between your intestine and skin, or between your intestine and another organ, such as the bladder or vagina. When internal fistulas develop, food may bypass areas of the bowel that are necessary for absorption. An external fistula can cause continuous drainage of bowel contents to your skin, and in some cases, a fistula may become infected and form an abscess, a problem that can be life-threatening if left untreated. Fistulas around the anal area (perianal) are the most common kind of fistula.
Anal fissure. This is a crack, or cleft, in the anus or in the skin around the anus where infections can occur. It's often associated with painful bowel movements. This may lead to a perianal fistula.
Malnutrition. Diarrhea, abdominal pain and cramping may make it difficult for you to eat or for your intestine to absorb enough nutrients to keep you nourished. Additionally, anemia is common in people with Crohn's disease.