How did wearing masks for Halloween start?

Answer 1

Back in the days when the Celts and Gauls were running the British Isles and a lot of Europe, the Celts celebrated Samhain (pronounced SOW-in, believe it or not). This means "Summer's End," and it was on November 1. The Celts believed that on the night before Samhain, the veil between our world and the underworld, netherworld, world of the dead, faerie, all of these sort of twilight realms, became very thin, and that it was possible for the denizens of each to cross over into the other. Afraid of who or what they might encounter from these other worlds, the Celts wore masks to frighten away these "boogens".