Diarrhea refers to the frequent passage of loose or watery unformed stools. As a rough guide, it can be said that three or four loose or watery stools a day can be considered as diarrhea. The disease may be acute or chronic. 

The intestine normally gets more than 10 liters of liquid per day which comes from the diet and from a secretion of the stomach, liver, pancreas, and intestines. In the case of diarrhea, water is either not absorbed or is secreted in excess by the organs of the body. It is then sent to the colon where the water holding capacity is limited. Thus, the urge to defecate comes quite often.

There are many and varied causes of diarrhea. The chief causes are overeating or eating of wrong foods, putrefaction in the intestinal tract, fermentation caused by incomplete carbohydrate digestion, nervous irritability, use of antibiotic medications and excessive intake of laxatives. Other causes include parasites, germs, virus, bacteria or a poison which has entered into the body through food, water or air. Allergies to certain substances or even common foods such as milk, wheat, eggs and seafoods and emotional strain or stress in adults and fright in children.

Diarrhea may be a prominent feature of organic disease affecting the small or large intestine such as the sprue syndrome, malignant disease, and ulcerative colitis. It may also result from operations on the gastrointestinal tract. Diarrhea may alternate with constipation. This may result from the irritation of the mucous membrane by impacted hard feces.

Diarrhea for prolonged periods can lead to certain complications. These may include weakening, due to loss of vitamins like A, D, E and K and other nutrients as food is rushed through the body without giving the nutrients a chance of being absorbed.