Loose bowel movements are commonly caused by a virus, such as the stomach flu, explains WebMD. Individuals may also suffer from loose bowel movements when they eat foods that upset the digestive system, use certain medications, have allergies to certain foods or possess a bacterial infection.
Individuals who have difficulty absorbing nutrients or abuse laxatives may experience loose bowel movements, according to WebMD. Additional causes of a watery and loose stool include alcohol abuse, diseases of the intestines such as an ulcerative colitis or Chrohn's disease, diabetes, and certain medications. People with an overactive thyroid or a diagnosis of cancer may experience loose bowel movements. Individuals undergoing radiation therapy or people recovering from surgery on the digestive system may have this problem as well. Some runners also experience loose bowel movements.
A medical professional should be consulted if loose bowel movements are bloody, black or appear to look like tar, WebMD advises. Individuals with a high fever that lasts longer than 24 hours or people who have severe pain in the rectum or stomach area should also contact a medical professional for a consultation. Medical attention is necessary when loose bowel movements accompany headaches, a fast heart rate, dark urine, nausea or vomiting that leads to dehydration.