Anal and rectal problems may also result from infectious or inflammatory causes. These include:

• Anorectal abscess. An abscess is an enclosed, infected cavity filled with pus. Anorectal abscesses typically develop in the deep mucus glands located in the wall of the anus or rectum. They may occur deep in the rectum or close to the skin around the anus. Abscesses near the skin may be visible as red, tender lumps. Most anorectal abscesses are caused by bacterial infections. Abscesses may eventually form an anorectal fistula, an abnormal channel in the anus or rectum.
  
  
• Proctitis. Inflammation of the lining of the rectum (rectal mucosa).  This may be chronic or acute. There may be a number of causes, including Crohn's disease and ulcerative colitis. Other causes include rectal injury, allergies, nerve malfunction, sexually transmitted diseases (e.g., gonorrhea, syphilis, chlamydia, herpes) and bacterial infection (e.g., salmonella). Radiation therapy and antibiotics may cause proctitis by changing the balance of naturally occurring bacteria in the rectum, called the intestinal flora, allowing other bacteria to grow in their place. Patients with weakened immune systems have an increased risk for proctitis.
  
  
• Inflammatory bowel disease (IBD). Chronic inflammation of the intestine. These conditions may affect the anus and rectum as well as other parts of the bowel. The primary types of IBD are ulcerative colitis and Crohn’s disease. Ulcerative colitis usually begins in the rectum or sigmoid colon and spreads to other areas of the colon. However, it may affect the rectum alone (ulcerative proctitis). Crohn’s disease and other forms of colitis may also inflame the rectum and colon.
  
  
• Anal warts. Cauliflower-like warts may develop on the skin around the anus. These are typically caused by an infection of condylomata acuminata, which is usually transmitted sexually.
  
  
• Anal and rectal cancer. Colorectal cancer may affect the anus and rectum. Anal cancers are very rare.