Main article: Hardmode#Spread
- Corruption, Crimson and Hallow will spread to Stone, Sand, Hardened Sand, Sandstone, Ice, and Grass (the "corruptible blocks"), turning them into their respective counterparts (Ebon-, Crim-, or Pearl- blocks, based on the biome). Only blocks up to three tiles away are susceptible of being converted.
- Crimson and Hallow vines (which can grow up to 10 tiles downward) can spread Crimson and Hallow when they come in contact with corruptible blocks below them. There are no Corruption vines.
- Corruption and Crimson are capable of converting Mud and Jungle Grass to Dirt which can then be converted to their respective grasses. Mud Blocks containing Mushroom grass are not affected and Hallow cannot convert Mud at all.
- Hallow and Corruption/Crimson cannot convert each other.
- Hallowed grass will convert Crimson grass, but still stops at all other Crimson blocks.