Physicists in the US have shown that plasmas can be used to kill the bacteria that cause tooth decay. John Goree and colleagues at the University of Iowa have used a hand-held "plasma needle", which works at room temperature, to kill Streptococcus mutans grown in a glass dish (J. Phys. D: Appl. Phys. 39 3479). Although the needle is only an experimental device at the moment, the researchers say it could one day be used by dentists to replace mouthwash as a much more efficient way of eradicating oral bacteria.