During digestion, food and water are moved through the intestines by smooth muscle that encircles the intestines and contracts or squeezes them. Normally, the food, water, and smooth muscle contraction work in balance together to produce a normal stool. Sometimes this balance can get upset, causing problems in the stool.
When the smooth muscle contracts too fast, there may not be enough time for much water to be absorbed in the intestines. When this happens, watery stools, called diarrhea, occur. If the contraction of the smooth muscle is really strong, you may end up with stomach cramps.
There are 2 main classifications of diarrhea—acute and chronic functional.
Acute diarrhea is the passage of 3 or more loose stools in one day. It usually lasts only 5 to 7 days and can be caused by common things such as a stomach virus, food poisoning, medicines, lactose intolerance, or artificial sweeteners.1
Some people may experience long-lasting diarrhea, called chronic functional diarrhea. Chronic functional diarrhea is the passage of 3 or more loose, mushy, or watery stools without pain lasting more than 4 weeks.2 There is usually no known cause of chronic functional diarrhea, but treatments exist to help manage the symptoms.