Jonathon Beckmeyer, assistant professor at the Indiana University School of Public Health-Bloomington, said the act of trick-or-treating has generally been associated with childhood, but some adults trick-or-treat without children.
"It could be some people trying to relive a childhood experience that was fun. Or, maybe they just like candy," Beckmeyer said in a statement. "Quite frankly, it probably makes people uncomfortable if you're in your 20s and you're coming trick-or-treating and don't have kids with you."
This might be more prevalent in college towns, where groups of students might dress up and go door-to-door together.
If a group of students wants to go, others will follow because "college students are still very socially based and peer-based and will support more of a collective desire to go trick-or-treating," Beckmeyer said.
However, in the last few years some towns in Illinois, Maryland, Mississippi and Virginia adopted age restrictions on trick-or-treating in fear of opening their doors to high school students and adults. These towns ban children age 12 and older from trick-or-treating, while other states adopted curfews for the holiday that don't go later than 9 p.m.
Beckmeyer said when adults partake in activities outside the norm, such as trick-or-treating alone or with other adults, it can call into question why these behaviors are happening.
"You have people who just want to try on a new identity, and they want to do something fun, so they go out and get dressed up," he said. "Just try to do it in a way that is going to be most appropriate for your age."