How did the wearing of costumes on Halloween start?

Answer 1

Well, it originated from Northern Europe traditions so probably from them. But they are worn to "Scare off the ghost and demons" but as the years passed by they just became something to wear when you go trick or treating. Nothing more to most people.

Answer 2

Many, many years ago, in times past, adults began dressing in elaborate costumes for Halloween parties, also known as Masquerade parties, long before it became an annual event for children. Dressing up in Halloween costumes is a recent tradition that developed in the twentieth century. The first store bought Halloween costumes were not available before the 1930's.