Experts claim the daily use of Listerine, particularly the Cool Mint flavor, could increase the risk of two deadly cancers. They advise against its everyday use. A recent study revealed that daily gargling with Listerine Cool Mint significantly increased the levels of two types of bacteria in the mouth, both of which have been linked to esophageal and colorectal cancer. The study, conducted by scientists from the Institute of Tropical Medicine in Antwerp, Belgium, found that the alcohol in the mouthwash disrupts the normal bacterial balance in the mouth.