(CNN) — When we look for fun things to do for Halloween, haunted houses are inevitably part of the list.
With their costumed players, spooky music and darkened rooms, they present a great way to get the daylights scared out of you.
But what most don't know is that a walk through a haunted attraction is a tradition that's been around for quite some time. The earliest known spooky house dates back to the early 1900s, but there isn't a lot of information about them for decades after that.
Over the decades, they've been wildly popular.
Scott Simmons, founder of the Pittsburgh-area haunted attraction The ScareHouse, has been involved in the haunted house business since he attended college in the 1970s.
"There's a whole generation of people growing up who have no idea how lucky they are to go to these Hollywood-quality haunted houses," Simmons told HLN. "We had to spread the word about our haunted houses by hoping people would tell their friends. We were viral before the Internet existed."
Simmons worked with friends in college to put together their first haunted house.
All the money raised was donated to local charities.
In the late 1960s and early '70s, the Junior Chamber International created Jaycees haunted houses, which were run by local chapters. As the haunted houses gained popularity and word about them spread to other branches of the youth organization, more and more kids wanted to take part, Simmons said.
As the haunted house evolved over the years from a simple act of kids dressed in sheets and jump scares to something a little more sophisticated, Simmons said the activities became even more popular, inspiring current attractions such as "The Basement," which is a more psychological-based horror exhibit in The ScareHouse.
"Terror on Church Street was a Florida haunted house that launched in the early '90s. It was much more elaborate than the houses before it and definitely not for kids," Simmons said. "That haunted house inspired a lot of people to push the envelope that much further."
Simmons said that his generation grew up with haunted houses, and as a result, enthusiasts like him and his friends grew up with the desire to make them bigger and better.
"I get to scare people for a living," he said.
Dr. Margee Kerr, a sociologist and "scare expert" who helps to manage The ScareHouse, told HLN that when it comes to how to frighten people, it's an ongoing study that is always fascinating for her. She's an adjunct professor at Pittsburgh-area colleges.
While people are scared of common things like zombies, clowns and the dark, there are also a host of things that work to keep haunted house attendees on their toes.
"The uncanny valley, which originated in 1906, still scares people to this day," Kerr said. "It's when something looks and acts like a human, but isn't [such as zombies]. And people also always react to body horror, such as people who look sick. It's a visceral reaction. When things aren't what they seem, we become scared that they could happen to us, too."
As for how far ScareHouse pushes the envelope, it tries to stay on the edge without crossing any lines that would disturb too deeply. Some haunted houses have offered experiences that simulate kidnapping and even rape..
'We don't want to traumatize people," she tells HLN. "We want them to come out and feel that they overcame. We don't exploit women or use things that could trigger trauma. That's not a good time."
Today, Simmons' ScareHouse celebrates its 15th year. Housed in an old bank-turned-lodge that used to house a gathering called "The Last Man's Club," the haunted house continues to draw big crowds every year. When it comes to scaring people, Simmons said that the reactions have stayed the same even though times have changed.
"We want people to scream and then laugh, have a good time," he tells HLN. "And that's exactly what they do. One thing is interesting though -- the audience keeps getting older. A few decades ago, it was all kids. Now those same kids are grownups that still want to come and have a good time."