If there's no obvious reason for a black stool (such as food, a supplement, or a medication like Pepto-bismol), it could be time to look for blood in the stool. 1  A variety of medical reasons can cause black stools that are also tarry with a foul smell.
1 Lungs, kidneys or liver. Inflammation may cause pneumonia, bronchitis or other problems in your lungs; may lead to problems with kidney function; and may cause hepatitis or cirrhosis in your liver.  Lymph nodes. A small percentage of people with Sjogren's syndrome develop cancer of the lymph nodes (lymphoma).
Sjogrenâs syndrome is a relatively common autoimmune disease that mainly affects the eyes and salivary glands, but can affect different parts of the body. Immune system cells, called lymphocytes, and autoantibodies attack the bodyâs moisture-producing glands. This results in dryness of the mouth, eyes or other tissues.