Caustic most commonly refers to:

Causticity, the property of being able to corrode organic tissue

• Sodium hydroxide, sometimes called caustic soda

• Potassium hydroxide, sometimes called caustic potash

• Calcium oxide, sometimes called caustic lime

Caustic may also refer to:

• Caustic (band), an American industrial/powernoise band

• Caustic (mathematics), the envelope of rays reflected or refracted by a manifold

• Caustic (optics), optic phenomenon due to light rays reflecting/refracting through curved surfaces/objects

• Caustic Graphics, a graphics technology developer, part of Imagination Technologies

• Caustic Window, an alias of Aphex Twin (electronic musician Richard D. James)

• A playable character in the battle royale game Apex Legends