Eilish co-wrote "Oxytocin" with her producer brother Finneas. The same sibling song-composition team wrote all the songs on Happier Than Ever
as well as her debut album, When We All Fall Asleep, Where Do We Go?
Speaking to Rolling Stone
about penning such sexual tracks with her brother, Eilish admitted, "We kind of have to plug our ears when we're writing about desire for other people because we're f---ing siblings."