Dressing up on October 31 is hardly a contemporary concept.
The tradition dates back more than 2,000 years when the ancient Celts believed that October 31 marked the end of one season and November 1 marked the start of the winter season. The druids, the primary religious order in that region during the period, felt that it was during this time that the veil separating the world of the living from that of the dead was at its weakest, enabling the souls of the deceased to visit the world. While some of these souls belonged to loved ones and were welcomed to join family members at the dumb dinner, others were evil spirits intent on harvesting fresh souls. During Samhain, the druids worked hard to keep the amount of damage done by the evil spirits to a minimum.
It was on this day (and night) that the druids donned costumes which were constructed out of animal skins and placed the heads of animals on their own head and engaged in very specific Samhain ceremonies. In addition to the skins, the costumes also consisted of straw, white robes/cloth, blackened faces (generally blackened with soot,) and veils. It’s believes that the costumes served two purposes.
The first, and most obvious was as a form of protection against evil spirits, though it’s unclear if the costume was intended to scare evil spirits away or if they were designed to trick the spirits into thinking that the costumed person was already dead and a member of the spirit’s posse. Many of the costumes involved candles and hallowed out turnips. Records indicate that some of the costumes were quite elaborate. There’s even an accounting of one costume that involved a head with a wired jaw. The man wearing the costume had rigged a system that allowed him to make the jaws snap at anyone who drew too close to him.
The second reason historians feel that costumes were donned during Samhain was to help get everyone in the mood and improve community involvement in the Samhain festival.
As Celtic celebrations were steadily replaced by more Christian beliefs and values, the practice of wearing costumes on October 31 faded, though there were still pockets of the world where people got dressed up. As individuals in these regions moved from Europe to the United States, they brought with them many of the Samhain/Halloween traditions. For some reason, these practices really took hold during the late 1800’s. Since then, the number of people who get dressed up for Halloween parties and trick-or-treating has steadily increased so that today, the Halloween costume industry is worth several million dollars.
“Halloween History.” Costume Cauldron. Web. Accessed 30 October 2017. http://www.costumecauldron.com/shop/halloween-costume/Halloween-History-sp-29.html
Owen, James. “First Halloween Costumes: Skins, Skulls, and Skirts.” National Geographic. 29 October 2009. Web. Accessed 30 October 2017. http://news.nationalgeographic.com/news/2009/10/091029-halloween-costumes.html