Many of the microbes that contribute to bad breath live on the tongue. Because the surface of this muscle is pebbled with tiny ridges and taste buds, it provides a deceptively large area for bacteria to live on, particularly since the root of the tongue extends far back into the throat. Scraping the tongue may help reduce halitosis, but a scraper can't reach everywhere.
A review of tongue scraping data published in the journal Evidence-Based Dentistry found that a total of two articles have rigorously addressed the use of tongue scraping to battle oral odor. In both studies, tongue scraping appeared to reduce the levels of volatile sulfur compounds (VSCs), which are molecules that give bad breath its smell.
However, while scraping caused less gagging that tongue cleaning with a toothbrush, the former did not eliminate VSCs.
Besides delivering no agents that neutralize odor molecules, tongue scrapers have a little area in which to operate. They cannot reach down the throat and are not intended to be used on the underside of the tongue, both of which are common microbial hideouts.
To kill the bacteria that cause oral odor, individuals may consider using a specialty breath freshening rinse that can get at hard-to-reach microorganisms.