As with much of Trench, "Chlorine" was written and produced by Tyler Joseph, the lead singer of Twenty One Pilots, and Paul Meany of Mutemath, who also provided part of the voice for the track's opening lines.

[4] The songwriting process and recording took place in secret in Joseph's basement studio in Columbus, Ohio, while the track was mixed by Adam Hawkins and mastered by Chris Gehringer at Sterling Sound, New York City.

[7] It is an electropop, trip hop and rap rock song featuring a lowered voice found on the band's previous album Blurryface and a "menacing, Zaytoven-esque piano twinkle".

[8][9][10][11][12] It has been described as a "menacing slow-burner" with an "annoyingly infectious" chorus comparable to the work of Bastille, Thom Yorke, DJ Shadow and Gym Class Heroes.

On January 22, 2019, fans of Twenty One Pilots began speculating that a music video for the song "Chlorine" would be released the following day due to a series of teasers that the band posted on social media, including a short clip of a dirty swimming pool soundtracked by a drum beat similar to the one found on the track.

[23] "Chlorine" pleased music critics, with positive sentiments being directed towards its catchiness and the band's increased songwriting maturity compared to their antecedent records.

Joshua Copperman of PopMatters complimented "Chlorine"'s musical restraint in comparison to the band's previous work and opined that it featured the "catchiest chorus on the record.

The video ends with Joseph sitting in an empty pool accompanied by the creature, whose antlers begin to shrink again, before offering it a cup containing an unknown substance, which Ned refuses to take.

[33] It is the first unplugged performance of a track from Trench to be released from the band's Location Sessions series, and is presumed to have been recorded at a private concert in Mexico City, where the coordinates in the song's title points.