What is bloody diarrhea? Bloody diarrhea is a potentially critical condition in which there is blood mixed in with loose, watery stools. The blood can arise from anywhere along your digestive tract, from the mouth to the anus. Bloody diarrhea is often a sign of gastrointestinal bleeding due to injury or disease. Diarrhea that contains bright red or maroon-colored blood may be referred to as hematochezia, while melena is used to describe black, tarry, and smelly diarrhea. Bloody diarrhea may also be referred to as dysentery, which is usually caused by a bacterial infection. Bloody diarrhea can occur in all age groups and populations. Depending on the cause, it can last for a short time (acute) and disappear relatively quickly, such as when it is due to a gastrointestinal infection. Bloody diarrhea can also recur over a longer period of time (chronic), such as when it is due to inflammatory bowel disease. Bloody diarrhea is a potentially life-threatening condition that should be evaluated in a medical setting. If you are also dizzy, weak, and vomiting blood, you should seek immediate medical care in an emergency setting.