There are unseen forces behind why a house might feel haunted — but no, it’s not ghosts.

New research suggests that inaudible infrasound waves emitted by a building’s old boiler, pipes, and plumbing can negatively influence someone’s mood, making them feel unnerved and uncomfortable. That could be enough to convince them there are ghosts afoot, especially if they’re already open towards supernatural explanations.

“What infrasound may do is supply a bit of bodily discomfort that a ghost or haunting explanation can then attach itself to,” Rodney Schmaltz, a psychologist at MacEwan University in Canada, and coauthor of a new study published in the journal Frontiers in Behavioral Neuroscience, told The Guardian. “For someone who is not inclined to think in terms of ghosts, the same sensation would probably just register as a stuffy, uncomfortable old building. For someone who is already primed, it might feel like proof of a spirit or presence.”

Infrasound is the term for sound at frequencies below 20 Hz. While this falls outside a human’s typical range of hearing, some research shows that we can subconsciously detect sound waves at these low frequencies.

Schmaltz previously tested his hunch in an experiment in which participants were asked to walk through a haunted house attraction with infrasound speakers placed throughout. When these speakers were activated, Schmaltz found, the participants walked through the building faster.

To more conclusively test whether infrared had a role in spooky sensations, the researchers recruited 36 volunteers to listen to either calming or unsettling music. During half of these tests, the researchers played infrasound without telling the participants. Afterwards, they gathered saliva samples from each of them.

Not only were the participants unable to tell when the infrasound waves were being emitted, but they acted more irritated and unsettled when they were, regardless of what music was playing, the researchers found. They also tended to rate both kinds of music as sadder than the participants that weren’t subjected to infrasound. But the most compelling finding was that the infrasound subjects had higher levels of cortisol in their saliva, a sign that their body’s stress response had kicked in.

“Whether they were listening to calming instrumental music or something more unsettling, the infrasound shifted their mood and their stress response in a negative direction,” Schmaltz told The Guardian. “In plain terms, you cannot hear infrasound, but your body and your mood appear to respond to it anyway, and the response tends to be unpleasant.”

Schmaltz speculates that the “low rumbling of pipes in the basement” and other weird building vibrations you’d expect from a decrepit, spooky location could produce the infrasound.

So have these meddling scientists unmasked the true culprit behind ghost sightings? They wouldn’t quite put it that way. The spine-tingling feeling that a building’s haunted more than likely arises from a number of factors, though infrasound could be a major one. And it doesn’t explain visual sightings of apparitions, either. Moreover, further tests would need to bear out whether popular “haunted” locations have notable infrasound levels, and if they are indeed produced by their ancient plumbing.

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