Acid is a hazardous chemical compound found throughout the Metroid series. Acid does harm to Samus' Power Suit at a rapid pace due to its corrosive effects. It also impedes her movement. Acid is mostly present on Zebes. Once Samus has acquired the Varia Suit in Metroid: Zero Mission, she becomes immune to the effects of acid. Certain creatures, such as the Mua and Geegas thrive in acid. Kraid's Hideout features enormous pools of acid, though some of these are actually fake and will disappear when Samus makes contact. Some creatures, like Kihunters, spit acid at Samus to damage her. Flaahgra was a mutant plant in Metroid Prime, mutated by the Phazon on Tallon IV. The creature polluted the Water in the Chozo Ruins to an acidic state until Samus killed the beast, which restored the water to its harmless state.
In Metroid Prime 3: Corruption, the Pirate Homeworld was doused in Acid Rain. Unlike Acid Rain on Zebes, Samus was not adapted to the environment and would be constantly damaged by the rain until she acquired the Hazard Shield. This may suggest that the level of acidity in the rain is different from acid on Zebes.
- The Purple liquid on planet SR388 was once hypothesized to be acid in Metroid II: Return of Samus, as revealed in the Super Game Boy Player's Guide. This was confirmed to not be the case with the release of the game's remake, Metroid: Samus Returns.
- There is an extremely harmful substance found mostly in Ridley's Lair in Super Metroid. This substance can also be found in Crateria as well as Tourian and bears a slight resemblance to acid. However, the Super Metroid Nintendo Player's Guide nevertheless refers to it as lava. Also, the fact that two of the mentioned areas are located near Zebes's core makes this substance, which ignores the Gravity Suit's protection, more than likely to be a superheated variant of lava and/or magma.
|Hazardous||Acid (Beta) • Acid Rain • Afloraltite • Dark Water • Fire • Fuel Gel • Lava • Phazon • Purple liquid|
|Gases||Dark vapor • Industrial-grade pesticide • Meta-viprium gas • Nohadin gas • Noxious gasses • Poison gas • Talvania Gas|
|Destructible|| Barnacle-like material • Bendezium • Brinstone • Cordite • Denzium • Frigidite • Glass • Grobnite • Ice • Maldium • Meltable Metal • Metroid webs • Radion • Sandstone • Talloric Alloy • Vegetation • Zebetite |
Kelbium and Zafrite
|Phazon||Red • Crystal • Black Crystal • Mass • Ore • Elite Nutrient Mix • Strain Vertigo • Phazite (Red) • Concentrated|
|Crystals||Ammolite/Witherite Shards • Black Phazon • Crystallized Fuel Gel • Crystals • Dark Sentinel • Lift • Liftvine • Light • Phazon • Red magma • Sentinel|
|Ore||Urthic • Phazon|
|Miscellaneous||Invisible platform • Jovian steel • Liquid Resource • Sand • Vaccine "Metroid" • Waste • Water • Yellow liquid|