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 disorder in which immune cells attack and destroy the exocrine glands that produce tears and saliva. It also associated with rheumatic disorders such as rheumatoid arthritis, and it is rheumatoid factor positive in 90 percent of cases. Sjogrens and hair loss.