The first study looking at the effect of chlorhexidine mouthwash on the entire oral microbiome has found its use significantly increases the abundance of lactate-producing bacteria that lower saliva pH, and may increase the risk of tooth damage. “In the face of the recent COVID-19 outbreak many dentists are now using chlorhexidine as a pre-rinse before doing dental procedures. We urgently need more information on how it works on viruses,” said one of the researchers.