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).
What Is Sjogren's Syndrome? When you have Sjogren's syndrome, your eyes, mouth, and other parts of your body get dried out. There are treatments that bring relief, though. It's natural to worry when you learn you've got a lifelong disease that will need regular care.