Cetylpyridinium chloride is a cationic quaternary ammonium compound in some types of mouthwash such as Crest Pro-HealthÂ®, ScopeÂ®, Reach ACTÂ®, CepacolÂ®, ViadentÂ®, OasisÂ®, Dr. FreshÂ®, swishÂ®, BreathRXÂ®, and BetaCellÂ®, toothpastes such as Crest SensitivityÂ® and Crest Plus ScopeÂ®, CepacolÂ® lozenges and throat sprays, anti-snore throat sprays (Breathe RightÂ®, Rite Aid, CVS, Walgreens, etc.), OasisÂ® moisturizing mouth spray, BreathRXÂ® breath spray, and SinoFreshÂ® and Ayr No-Drip SinusÂ® nasal sprays. It is an antiseptic that kills bacteria and other microorganisms. It has been shown to be effective in preventing dental plaque and reducing gingivitis. It has also been used as an ingredient in certain pesticides. However, this ingredient has also been shown (according to WebMD, eMedicine, and Amazon.com and Drugstore.com reviews of Crest Pro-HealthÂ® rinse product) to cause brown stains between the teeth.