Hello I appreciateyourconcern bleeding bowel movement is a matter of worry at younger age like your son This could be due to any of following Acid peptic disease or peptic ulcer rectal polyp ateriovenous malformations or fistula liver disease like cirrhosis Colon cancer in my opinion you should take him to the gastroenterologist for endoscopy and confirmation of diagnosis meanwhile anti acidity medicines like pantoprazole or omeprazole with antacids will definitely help him avoid smoking and alcohol have fresh fruits and lots of water Hope.this helps him best wishes