Blood in the stool can come from anywhere in the digestive tract, such as the stomach or intestines. Depending on where the blood is coming from and how fast it is moving, it may be bright red, reddish brown, or black like tar.
A little bit of bright red blood on the stool or on the toilet paper is often caused by mild irritation of the rectum. For example, this can happen if you have to strain hard to pass a stool or if you have a hemorrhoid.
A large amount of blood in the stool may mean a more serious problem is present. For example, if there is a lot of blood in the stool, not just on the surface, you may need to call your doctor right away. If there are just a few drops on the stool or in the diaper, you may need to let your doctor know today to discuss your symptoms. Black stools may mean you have blood in the digestive tract that may need treatment right away, or may go away on its own.
Certain medicines and foods can affect the color of stool. Diarrhea medicines (such as Pepto-Bismol) and iron tablets can make the stool black. Eating lots of beets may turn the stool red. Eating foods with black or dark blue food coloring can turn the stool black.
If you take aspirin or some other medicine (called a blood thinner) that prevents blood clots, it can cause some blood in your stools. If you take a blood thinner and have ongoing blood in your stools, call your doctor to discuss your symptoms.