Although many believe that plastic cutting boards are safer to use than wooden ones—no juices seeping into the grooves with plastic, right?—there's actually no evidence to back up those claims. The main benefit to plastic seems to be that its nonporous surface can be doused with boiling water for disinfecting without causing any harm to the actual board.
Wooden cutting boards pulled the bacteria down beneath the surface of the cutting board, where they didn’t multiply and eventually died off. Even older wooden cutting boards with deep grooves had low levels of recoverable bacteria, similar to what was found in new boards. While new plastic chopping boards can be cleaned and disinfected to the point where few bacteria remain, the same cannot be said for old knife-scarred boards.