Hello! Thank you for the query. Without such information like when has it tarted, is there any blood in the stool, any weight lost, abdominal pain, it is hard to give precise answer or solution. His symptoms may be caused by some gastrointestinal infection, food intolerance or allergy or even Crohns disease. For sure it is not a symptom which should be ignored. He should visit gastroenterologist and have proper diagnostics. Stool test, stool culture test, abdominal ultrasound, blood work, liver tests, pancreas tests should be done at first. Colonoscopy should be considered. Hope this will help. Regards.