Blindness is a harmful (negative) status effect in Minecraft Java Edition 1.21.
minecraft:blindness
Give Blindness II for 60 seconds (Java Edition 1.13+; duration in seconds, then amplifier where 0 = level I):
Remove the effect from the nearest player:
Blindness shrinks your vision to a few blocks, disables sprinting and critical hits, and in vanilla survival it essentially never appears naturally.
No survival mob or potion applies Blindness in current Java Edition; it is command-only content. The unused illusioner mob applies it in its unused raid behavior, and map makers trigger it with /effect for horror sequences.
If you meet Blindness on a server or map, remember it blocks sprinting and crits, so fighting through it is genuinely harder, not just darker. Milk clears it instantly.
The effect ID for Blindness is minecraft:blindness. Java Edition 1.13+ /effect commands use this namespaced form. On Java 1.12.2 and earlier the numerical ID was 15.
Run /effect give @p minecraft:blindness 60 1 to get Blindness II for 60 seconds. The first number is the duration in seconds; the second is the amplifier (0 = level I, 1 = level II). Remove it with /effect clear @p minecraft:blindness.
Blindness is a harmful (negative) status effect in Minecraft Java Edition, based on its registry category (harmful).
In vanilla Java Edition survival, you do not; Blindness is applied only through commands or custom content. The illusioner, an unused mob, would inflict it if enabled.
It also prevents sprinting and landing critical hits, which makes it a combat-relevant effect in maps and PvP scenarios, not just a visual handicap.