The song failed to reach the heights of previous single "Foundations" both commercially and critically. It managed to peak just outside the top twenty of the UK Singles Chart upon its physical release.Slant Magazine felt the song failed to live up to "Foundations", while The Guardian felt overall the song was "unnecessary".
The music video for "Mouthwash" was shot at the Bristol Hippodrome with the cast of the Starlight Express, who learned two new routines for the video. It features Nash backstage of the theatre, and on stage playing the piano while the show is being performed. The video was directed by Kinga Burza.