Constipation means different things to different people. For many people, it simply means infrequent stools. For others, however, constipation means hard stools, difficulty passing stools (straining), or a sense of incomplete emptying after a bowel movement. The cause of each of these types of constipation probably is different, and the approach to each should be tailored to the specific type of constipation. Constipation can also alternate with diarrhea. This pattern is more commonly considered as part of the irritable bowel syndrome (IBS). At the extreme end of the constipation spectrum is fecal impaction, a condition in which stool hardens in the rectum and prevents the passage of any stool. The number of bowel movements generally decreases with age. Ninety-five percent of adults have bowel movements between three and 21 times per week, and this would be considered normal. The most common pattern is one bowel movement a day, but this pattern is seen in less than 50% of people. Moreover, most people are irregular and do not have bowel movements every day or the same number of bowel movements each day. Medically speaking, constipation usually is defined as fewer than three bowel movements per week. Severe constipation is defined as less than one bowel movement per week. Common causes of constipation include pain medications (especially narcotics), dehydration, depression, stroke, diseases of the nervous system, diseases of the abdomen, colon cancer, travel, Hirschsprung's disease, and scleroderma. Complications of constipation include hard stools, anal fissure, anal tears, rectal bleeding, hemorrhoids, abdominal discomfort, abdominal swelling, abdominal pain, bloating, and aggravation of hernias.