People exposed to infrasound may not consciously hear it, but they can show higher cortisol levels and increased irritability, which may help explain reports of “haunted” locations.
Infrasound refers to sound at very low frequencies, below 20 Hertz (Hz), a range that people usually cannot hear. It can be produced by natural events such as storms, as well as human made sources such as traffic. Some animals use infrasound for communication, while others move away from it. In a new study of whether people can sense infrasound, scientists found that although humans do not consciously detect it, their bodies still react, with exposure linked to greater irritability and higher cortisol levels.
“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 in Frontiers in Behavioral Neuroscience. “Many people are exposed to it without knowing it. Our findings suggest that even a brief exposure may shift mood and raise cortisol, which highlights the importance of understanding how infrasound affects people in real-world settings.
“Consider visiting a supposedly haunted building. Your mood shifts, you feel agitated, but you can’t see or hear anything unusual. 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.”
Sound of the underground
The researchers recruited 36 people and asked each of them to sit alone in a room while either calming or unsettling music played. Half of the participants were also exposed to hidden subwoofers producing infrasound at 18 Hz. Afterward, they described how they felt, rated the emotional tone of the music, and said whether they believed infrasound had been present. They also provided saliva samples before and after the listening session.
Participants who had been exposed to infrasound showed higher salivary cortisol levels. They also reported feeling more irritable, less interested, and more likely to perceive the music as sad. Even so, they could not reliably tell whether infrasound had been playing.
