Reaction

Reaction may refer to a process or to a response to an action, event, or exposure.

Physics and chemistry

 * Chemical reaction
 * Nuclear reaction
 * Reaction (physics), as defined by Newton's third law
 * Chain reaction (disambiguation)

Biology and medicine

 * Adverse drug reaction
 * Allergic reaction
 * Reflex, neural reaction
 * Hypersensitivity, immune reaction
 * Intolerance (disambiguation)
 * Light reaction (disambiguation)

Psychology

 * Emotional, reaction
 * Reactivity
 * Proactivity, opposite of reactive behaviour
 * Reactive attachment disorder

Politics and culture

 * Reactionary, a political tendency
 * Reaction video
 * Commentary (disambiguation)

Proper names and titles

 * Reaction (album), a 1986 album by American R&B singer Rebbie Jackson
 * "Reaction" (song), the title song from the Rebbie Jackson album
 * "Reaction", a single by Dead Letter Circus
 * Reactions, a 2018 album by The Mods
 * ReAction GUI, a GUI toolkit used on AmigaOS
 * Reaction.life, a political news and commentary website edited by Iain Martin
 * Reaction Records, a record label
 * TNA Reaction, a former documentary show of TNA Wrestling (now known as Impact Wrestling) behind the scenes
 * Reaction (The Spectacular Spider-Man), an episode of the American animated television series The Spectacular Spider-Man
 * The Reaction, a novel in the Animorphs series
 * Reactions (journal), a chemistry journal published by MDPI