"Chlorine" is a song written and recorded by the American musical duo Twenty One Pilots. The song was released on October 5, 2018 as part of their fifth studio album, Trench, by Fueled by Ramen and on January 22, 2019 as the fifth single from the album plus a music video. It became the band's fifth number one single on the Billboard Alternative Songs chart and the first track from Trench to be certified platinum. The song was sent to Alternative radio on January 29, 2019 then sent to Top 40 radio on March 19, 2019. The track was written and produced by lead singer Tyler Joseph and Paul Meany of rock band Mutemath. It is a pop, electropop, trip hop and rap rock song which discusses "how creativity can cleanse dark impulses but cause its own pain".
"Chlorine" was well received by music critics, who highlighted its catchiness and musical restraint compared to the band's previous work. Upon the song's release as a single, a music video directed by Mark Eshleman of Reel Bear Media was uploaded. The track is the duo's most popular from Trench.