What commonly causes loose stools in adults?

Not always diarrhea: Stool texture (regardless of volume or frequency of movements) is defined by the bristol stool scale (bss), which ranges from 1 (hard, pellet stool) to 7 (loose, watery stool). Normal stool grades a 4 on the bss. On the other hand, "diarrhea" is defined by volume and stool frequency (typically more than 4-5 bowel movements/day). Tell your doctor as well about bleeding, fever, tenderness, & pain.