Imagine you’re in an old building and you feel a chill go down your spine. Could it be ghosts? This feeling may actually be caused by infrasound—low-frequency sound waves outside the range of human hearing.
Recently, scientists at MacEwan University in Canada asked 36 volunteers to sit alone in a room and listen to either calm or spooky music. While listening, half of the participants were also exposed to infrasound. No matter whether the music was peaceful or eerie, volunteers exposed to infrasound reported feeling more irritated and had higher levels of cortisol—a hormone, or chemical messenger, that’s linked to stress.
Old pipes, heating, and air-conditioning systems can produce infrasound, which may make some buildings feel spookier. “People may think a house is haunted,” says Rodney Schmaltz, one of the researchers on the study. “But often there’s a rational explanation.”