That uneasy feeling many people report in older buildings may have a measurable physical trigger, according to new research into infrasound, a type of low-frequency vibration that sits below the threshold of human hearing.
Scientists say these vibrations can be produced by everyday sources such as ventilation systems, traffic, and industrial machinery, and may be especially common in basements where aging pipes and mechanical equipment can generate persistent low-frequency motion.
In a controlled experiment published in Frontiers in Behavioral Neuroscience, researchers tested whether people could detect infrasound and whether it affected mood. The team focused on 18 Hz, a frequency below 20 Hz that most people cannot consciously hear.
The study involved 36 participants who sat alone in a room while listening to either calming or unsettling music. For half of the group, hidden subwoofers also generated infrasound during the session.
Afterward, participants rated how they felt and whether they believed infrasound had been present, and researchers collected saliva samples to measure cortisol, a hormone associated with the body’s stress response. The key question was whether the body would react even when the sound could not be consciously identified.
Participants exposed to infrasound showed higher salivary cortisol levels and reported feeling more irritable and less engaged, the researchers found. They were also more likely to describe the music as sad, despite being unable to reliably tell whether infrasound had been playing.
A hidden factor behind haunted vibes
Researchers argue the results help explain why some spaces feel disturbing without an obvious cause. In an old building, low-frequency vibrations from ventilation or plumbing may subtly influence mood, increasing tension without providing a clear sensory signal to blame.
The team noted that expectations can shape how people interpret discomfort, such as attributing agitation to paranormal activity after being told a building is haunted. In that context, infrasound offers a non-supernatural mechanism that still produces real, measurable effects.
What the study does not prove
The researchers cautioned that the study was relatively small and tested a single frequency over a short exposure, leaving open questions about how different frequencies, combinations, and longer durations might affect people. Real-world infrasound is rarely a clean tone, and its intensity can vary widely by environment.
They also emphasized that the biological pathway is not yet clear, even though the hormonal and mood shifts were detectable. Future work is expected to examine a broader range of conditions and to track responses during exposure, not only afterward.
Why long-term exposure matters
Cortisol plays a normal role in helping the body respond to challenges, but sustained elevation has been linked in broader medical research to health risks, including effects on sleep, mood, and cardiovascular function. The study adds to concerns that chronic, unnoticed low-frequency noise could contribute to ongoing stress in some settings.
Researchers say clearer evidence could eventually inform building design choices and noise guidelines, particularly around mechanical systems that generate low-frequency vibrations. For now, they suggest that if a room feels inexplicably tense, the cause may be structural and mechanical rather than mysterious.
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