We've all been there: you're in a dusty old basement, the air feels heavy, and you can't shake the sense that something is watching you from the shadows. But according to a new study published in Frontiers in Behavioral Neuroscience, the culprit might not be a ghost - it's probably just the building's plumbing vibrating at a frequency your body hates.
That creepy sensation, scientists say, could be caused by infrasound - extremely low-frequency sound waves below 20 Hertz (Hz) that humans can't consciously hear. These vibrations come from natural sources like storms and human-made ones like traffic, industrial equipment, and, yes, aging ventilation systems. While some animals use infrasound to chat with each other, humans apparently just get irritable.
"Infrasound is pervasive in everyday environments, appearing near ventilation systems, traffic, and industrial machinery," said Prof Rodney Schmaltz of MacEwan University, senior author of the article. "Many people are exposed to it without knowing it." He added that a visit to a supposedly haunted building might leave you feeling agitated for no obvious reason. "In an old building, there is a good chance that infrasound is present, particularly in basements where aging pipes and ventilation systems produce low-frequency vibrations. If you were told the building was haunted, you might attribute that agitation to something supernatural. In reality, you may simply have been exposed to infrasound."
To test this, researchers recruited 36 participants and had them sit alone in a room listening to either calming or unsettling music. For half of the group, hidden subwoofers secretly blasted infrasound at 18 Hz. After the session, participants reported how they felt, rated the music's emotional tone, and guessed whether infrasound had been playing. The researchers also collected saliva samples before and after to measure cortisol levels.
The results were clear: infrasound exposure led to higher cortisol levels and more self-reported irritability. Participants also found the music sadder and felt less engaged. But here's the kicker: they couldn't reliably tell whether infrasound was even playing. "Participants could not reliably identify whether infrasound was present, and their beliefs about whether it was on had no detectable effect on their cortisol or mood," said Schmaltz.
First author Kale Scatterty, a PhD student at the University of Alberta, noted that while irritability and cortisol are naturally linked, "infrasound exposure had effects on both outcomes that went beyond that natural relationship." So it's not just in your head - it's in your endocrine system.
The exact biological mechanism remains a mystery, but the researchers caution that long-term exposure could keep cortisol levels elevated, potentially harming mental and physical health. "Increased cortisol levels help the body respond to immediate stressors by inducing a state of vigilance," said Prof Trevor Hamilton of MacEwan University, corresponding author. "This is an evolutionarily-adapted response that helps us in many situations. However, prolonged cortisol release is not a good thing."
Because the study was small, the team ran additional analyses to confirm their findings, which held up for moderate to large effects. But larger and more diverse studies are needed. "So far, we've only tested a specific frequency," said Scatterty. "There could be many more frequencies and combinations that have their own differential effects."
Schmaltz, who studies pseudoscience and misinformation, offered a practical takeaway: "The next time something feels inexplicably off in a basement or old building, consider that the cause might be vibrating pipes rather than restless spirits." So go ahead, call an exorcist - but maybe call a plumber first.