WORCESTER, Mass. - Halloween wasn't always candy, costumes, and spooky decorations...

"The roots of Halloween go all the way back to the ancient Celtic festival of Samhain which was a celebration that marked the transition from harvest to winter and from one year to another," said Lauren Crockett-Girard, a visiting assistant professor at Assumption University

Crockett-Girard is a lover of not just cultural studies, but the supernatural and all things scary too. Her dissertation at Boston College was based on zombies and the meaning behind them metaphorically.

She says Samhain was believed to be a time where the veil between the living and the dead was thinnest. Many would refer to it as "Mischief Night," which ultimately changed how mostly everyone in America celebrated.

"Somewhere around the 1920s/1930s, when trick or treating originated as an alternative to a night of shenanigans where kids would go out, cause problems, pull pranks on people," she said.

Come the middle of the 20th century, Crockett-Girard says mass market Halloween costumes exploded in popularity, as did the candy industry, and the holiday became more like what we see today.

She points a number of factors behind the boom of Halloween. One of them being the ability to get scared in a safe and controlled environment. She says this is why many people, like herself, are also fond of horror movies. Crocket-Girard says nostalgia is also a major factor in the success of Halloween. She says for some, the ability to dress up in a costume on a cold October night can bring them back to being a yound child once again. Lastly, she says there's a community-building quality surrounding the holiday, which is another reason why Halloween has become the billion-dollar goliath it is now.

"As a holiday, right, it emphasizes coming together whether that be through trick or treating and meeting your neighbors, through Halloween parties, through spooky horror nights," Crockett-Girard said.

Survey data from the National Retail Federation shows consumer spending this Halloween is expected to reach a whopping $13.5 billion, with the average spending per person expected to be around $115. Costumes, decorations, and candy are all expected to bring in more than $4 billion each.

Despite the shift in how many Americans celebrate Halloween, Crockett-Girard says many who practice Paganism still recognize Samhain in a more traditional manner.