The cause of ulcerative colitis (UC) is unknown. It is believed to involve an overactive immune system that, once triggered to attack bacteria or viruses within the digestive tract, is unable to turn itself off. This continual attack within the large intestine leads to inflammation and irritation of the intestinal walls.

The disease seems to occur equally as often in men as it does in women. Although it is unclear why, when UC occurs among older populations (e.g., people in their 50s and 60s), it tends to be diagnosed more often in men than in women.

Certain factors appear to increase the risk of developing UC. These include:

• Heredity. UC appears to run in families. Approximately 20 percent of patients with UC have a blood relative with some form of inflammatory bowel disease (IBD), according to the Crohn’s & Colitis Foundation of America (CCFA).
  
  
• Age. Young people, especially those between the ages of 15 and 35, are more likely to develop UC, although UC may also occur in older or younger populations.
  
  
• Race and ethnicity. Whites have a higher risk of developing UC than non-whites. The risk of the disease is greater for people with a Jewish ethnic background (especially those of European descent) than other ethnic groups.
  
  
• Environment. UC appears to be a disease of the developed world, occurring primarily in the United States and Europe. It is unclear whether lifestyle (e.g., diet) or possible toxic exposure (e.g., pollutants) in these areas of the world may be related to UC. The risk of UC appears to increase for those living in urban areas and in northern climates.
  
  
• Cigarette smoking. Nonsmokers are more likely to develop UC than smokers. For Crohn’s disease (CD) (the other major type of IBD), it is just the opposite – smokers are more likely to develop or experience aggressive forms of CD. However, it is not recommended that patients smoke in order to lessen their risk of UC. It is unclear why smoking appears to decrease the risk of UC.

Factors that may trigger or aggravate UC symptoms include:

• Medications (e.g., antibiotics)
• Infection
• Hormonal changes
• Lifestyle changes
• Stress
• Diet