Diarrhea can happen from various sources:
Diarrhea by itself is not dangerous. Because the stool is watery, it can cause a lot of water to leave the body and result in dehydration which can be dangerous, especially to children and the older population.
Bloody diarrhea is caused by internal bleeding within the digestive tract. Sometimes the diarrhea is not related to the bleeding as they may be coincidental, as when for example the diarrhea may result of some food intolerance or bacteria, and the blood may result from hemorrhoids around the colon.
To most people, bloody diarrhea is very scary and uncomfortable. In most cases, medical attention should be sought.
Common temporary diarrhea does not usually need treatment as it goes away on its own. In cases of chronic diarrhea caused by digestive diseases or bacteria, treatment varies on the type of illness that is causing the chronic diarrhea.