Researchers from the College of Dentistry at the University of Illinois at Chicago say compounds in tea can slow the growth of bacteria in our mouths, which is the primary cause of bad breath. The magic ingredients are antioxidants called polyphenols, and they are found in both green and black teas.   It's the bacteria that live on the back surface of the tongue and in the deep pockets between the gums and teeth that make our breath smell bad. The bacteria "make horrible, smelly stuff," lead study author Christine D. Wu explained to Reuters in an interview. "That's why we get bad breath."