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).
Sjogren's syndrome is an autoimmune disease. This means that your immune system attacks parts of your own body by mistake. In Sjogren's syndrome, it attacks the glands that make tears and saliva. This causes a dry mouth and dry eyes. You may have dryness in other places that need moisture, such as your nose, throat, and skin. Sjogren's can also affect other parts of the body, including your joints, lungs, kidneys, blood vessels, digestive organs, and nerves.