 [ Symptoms ] causes of dark brown stool  i just passed a dark brown stool not black but pretty dark brown i was constipated as well i had not gone to the bathroom in almost two days i am a college student so i do not have a very nourishing diet at all no diarrhea slight dull abdominal pain  but i think that may just be my mind worrying about it too much [ Disease ] obviously i cannot examine you son but he most likely has adolescent gynecomastia a hormonal side effect of good ol puberty yes these can be tender ibuprofen may help and obviously he should avoid trauma to this area or trauma from teasing brothersfriends who like to pinch them or give him a painful twister or purple nurple ask you son and he will explain what this is these things can add to the normal discomfort of course research adolescent gynecomastia on the internet if you are concerned you can see his regular medical provider for a consultation