A small controlled experiment reported in Frontiers in Behavioral Neuroscience found that exposure to infrasound—ultra-low-frequency vibration below the range of human hearing—was associated with higher salivary cortisol and more negative mood ratings, even though participants could not reliably detect when the infrasound was present.
Infrasound refers to very low-frequency sound waves—typically below 20 Hertz (Hz)—that are generally outside the range of human hearing. It can be generated by natural phenomena such as storms and by human-made sources including traffic and industrial equipment.
In a study published in Frontiers in Behavioral Neuroscience, researchers tested whether infrasound can affect people even when they do not consciously perceive it. The experiment recruited 36 participants and used a between-subjects design in which participants listened to either calming or unsettling music, with some sessions also including an approximately 18 Hz infrasound tone delivered via hidden subwoofers.
After the listening session, participants reported their mood and rated the emotional tone of the music. Saliva samples taken before and after the session were used to measure cortisol, a hormone commonly linked with stress.
The researchers reported that participants exposed to infrasound showed higher salivary cortisol and, on average, rated themselves as more irritable. They also reported greater disinterest and were more likely to appraise the music as sad. Despite these changes, participants did not reliably identify whether infrasound had been playing, and the study reported no evidence that participants’ beliefs about its presence explained the mood or cortisol results.
The study’s senior author, Prof. Rodney Schmaltz of MacEwan University, said in a release accompanying the paper that infrasound is “pervasive in everyday environments,” including around ventilation systems, traffic, and industrial machinery, and that brief exposures may be enough to shift mood and raise cortisol.
In the same release, Schmaltz suggested that low-frequency vibrations in older buildings—especially in basements where aging pipes and ventilation systems may produce vibrations—could contribute to feelings of agitation that some people interpret as paranormal. The authors and accompanying materials also emphasized that larger and more diverse samples will be needed to clarify how broadly these findings apply outside the laboratory and in everyday environments.